Looking for a cheesy vegetable gratin to go with everything from rotisserie chicken to Easter ham? This tender rutabaga and butternut squash casserole is one of the best. I use thinly sliced root vegetables with leeks and fennel in this baked butternut squash recipe. The roasted rutabaga and butternut slices get tender and sweet nestled in a mix of creamy white sauce and cheese.
This post has been updated for recipe, photos and content since its original publication in 2017.
Table of Contents
- 1 Butternut squash is so versatile.
- 2 Ingredients you’ll need for rutabaga and butternut squash casserole
- 3 Components for the butternut squash casserole
- 4 Melting Leeks and Fennel for the baked Butternut squash recipe
- 5 How to make béchamel for the vegetable gratin
- 6 How to prep root vegetables for the casserole
- 7 Assembling the rutabaga butternut squash casserole
- 8 Why is my vegetable gratin watery?
- 9 Swaps & Substitutions
- 10 FAQ’s
- 11 What to serve with root vegetable gratin
- 12 Tender Butternut Rutabaga Gratin
Butternut squash is so versatile.
I always seem to have a butternut squash sitting on my kitchen counter because it goes well with so many things and my family loves it.
In this butternut squash casserole, it adds a light honeyed note that plays well with the vegetal quality of roasted rutabaga.
Honestly though, butternut squash is a mainstay for me because of its versatility.
I use this bulbous veg in everything from my Thai squash soup to this sausage and pumpkin favorite. Butternut squash puree makes my macaroni and cheese a little healthier, sweeter and gives it that neon-orange “Velveeta-like” hue.
It’s also cheap, plentiful and good for you! Can’t beat that!
Ingredients you’ll need for rutabaga and butternut squash casserole
- Butternut Squash
- Cheese or a Cheese Blend
- Olive Oil
- Kosher Salt
- White Pepper (optional)
- Black Pepper
- Dried Mustard
- Garlic Powder
Components for the butternut squash casserole
This is a simple baked butternut squash recipe, but there are a few components that need to be prepped before assembling the vegetable gratin. starting with the leeks and fennel.
Leeks are a root vegetable related to onions and other alliums but with a softer milder flavor, especially when cooked slowly over a low heat. Simmered gently with a little oil and/or butter and a pinch of salt, will release leeks natural moisture and bring out their sweetness.
It’s important to clean leeks well before using them as there’s often dirt and detritus that grows between their layers.
To clean leeks:
- Remove the root end and cut away the dark, woody leaves, leaving only the white and pale green parts.
- Slice the leeks crosswise into 1/4″-1/2″ slices and transfer to a bowl of cold water.
- Separate the rings of leek and swish them with your hand to dislodge any dirt. (Dirt will sink to the bottom).
- Lift the leeks out of the water and transfer to a salad spinner to dry.
Fennel is a perennial herb with spindly fronds and a bulbous stem. The bulb and fern-like fronds are edible, but the stems tend to be tough, so I don’t recommend using them. Fennel has a light licorice or anise flavor that’s more pronounced when served raw and softens when cooked.
To trim leeks:
- Cut away the stems and fronds.
- Slice the bulb into quarters, vertically and cut away the tough inner core.
- Lay the fennel flat on a cutting board and cut 1/4″ slices.
Melting Leeks and Fennel for the baked Butternut squash recipe
Ok, so you’re not actually “melting” these veggies. However, cooking them with a little fat and salt, in a covered skillet over a low heat, will soften the root vegetables to the point where they slump and don’t fight back. Here’s how to do it.
- Add butter and olive oil to a wide skillet with a tight fitting lid and heat over medium to medium-low heat.
- Add the sliced leeks and fennel and sprinkle with kosher salt, pepper and thyme.
- Stir to combine, cover and simmer for 10-12 minutes, stirring occasionally until the root vegetables are very soft and tender.
You don’t want to cook on a high heat, as that will brown the veggies. Be patient and go low and slow.
A béchamel is just a fancy name for a creamy white sauce. It’s what I use for my scalloped potatoes and as the base for my cheese sauce in my macaroni and cheese. Béchamel sauce is thick and creamy and really simple to make.
How to make béchamel for the vegetable gratin
- Melt the butter in a saucepan over medium to medium high heat.
- Sprinkle in the flour, salt, white pepper (if using), mustard powder and garlic powder and stir together until it forms a bubbly paste and there’s no dry bits of flour. Cook for about one minute, stirring constantly. (This mixture is called a roux, and it will help to thicken the sauce).
- Add warm milk a little at a time to the flour mixture, stirring constantly. (It will be thick and pasty at first, but just continue to stir and add milk. The roux will melt into the milk.
- Continue to stir constantly as you bring the mixture to a rolling boil and cook for one minute, then remove from the heat and set aside.
The sauce is lush and creamy. As it sits, it may develop a “skin”, but just give it a quick stir to blend it back into the béchamel.
How to prep root vegetables for the casserole
- Peel the butternut squash and rutabaga and trim away the ends.
- Slice the butternut squash in half vertically, and scoop out the seeds. Discard.
- Slice the rutabaga and butternut squash into very thin slices. (Note: rutabagas tend to be a little harder than the squash, so I recommend cutting the rutabaga in half and laying them flat side down, to give you a solid base to slice.
You want the butternut squash and rutabaga to be roughly the same thickness so that they bake in the oven at about the same time.
Layer the vegetable gratin in a 2-quart casserole dish.
Assembling the rutabaga butternut squash casserole
- Spread about 1/3 cup of the white sauce on the bottom of the casserole dish, then layer the rutabaga and butternut squash slices (alternating for color) to cover the bottom of the dish.
- Top evenly with 1/3 of the melted leeks and fennel.
- Sprinkle on 1/3 of the cheese and 1/3 of the remaining bechamel sauce.
- Repeat the layers 2 more times finishing with bechamel and cheese.
- Cut a piece of foil large enough to cover the gratin dish and spray it with vegetable spray (to prevent the cheese and sauce from sticking to the foil when you’re baking the butternut squash casserole.
- Bake at 375° F for one hour.
- Reduce the heat to 350° F and remove the foil.
- Continue to bake the vegetable gratin for 25-30 more minutes or until bubbly and lightly browned.
Why is my vegetable gratin watery?
Though butternut squash and rutabaga don’t seem to have much liquid when you’re prepping them, there’s a surprising amount of moisture that will seep out during baking.
Pro-Tip: After the gratin sits for a few minutes, you’ll notice watery puddles around the edges. It’s fine, but if you want to remove it, scoop it off with a spoon or use a turkey baster to suck up excess moisture.
Swaps & Substitutions
Though the rutabaga and butternut squash are delicious in this vegetable gratin, you can also substitute other root vegetables.
- Swap Yukon Gold potatoes for the rutabaga or butternut squash.
- Use sweet potatoes instead of the squash.
- Try sliced turnips instead of rutabaga.
- Use other types of winter squash like acorn, delicata or baby pumpkin.
Yes. Assemble it up to one day in advance and keep refrigerated until you’re ready to bake. Remove from the refrigerator about 30-45 minutes before baking, so it has a chance to come to room temperature. Putting a cold casserole in the oven may add another 15-20 minutes of overall baking time to the recipe.
Reheat the vegetable gratin covered in a 325° oven for 20-25 minutes. Remove the foil and continue to heat for an additional 5-10 minutes until hot.
No, this recipe doesn’t freeze well.
What to serve with root vegetable gratin
- Cider Brined Smoked Pork Loin
- Grilled Herb Crusted Rack of Lamb
- Marinated Roast Turkey Breast
- Beer Can Chicken
- Grilled Veal Chops
- Rotisserie Chicken At Home
- Bourbon Marinated Grilled Flank Steak
- Herb Roasted Chicken with Pan Gravy
- Pan Roasted Chicken Breasts with Mustard Sauce
- Homemade Roast Beef with Onion Gravy
More vegetable gratins you’ll love:
- Kale Barley Mushroom Gratin
- Cauliflower Mustard Gratin
- Creamy Chayote Gratin
- Savory Sweet Potato Casserole
- Cauliflower and Mushroom Gratin
- Kale and Butternut Squash Gratin
- Twice Baked Sweet Potato Gratin
- Cheesy Tomato and Egg Gratin
- Potato Ham Au Gratin
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Tender Butternut Rutabaga Gratin
FOR THE MELTED FENNEL AND LEEKS:
- 2 leek white and pale green parts only
- 1 bulb fennel cored and thinly sliced
- 2 teaspoons olive oil
- 2 teaspoons butter
- 2 teaspoons fresh thyme minced
- ¼ teaspoon kosher salt
- 1 pinch black pepper
FOR THE BECHAMEL:
- 3 tablespoons butter
- 3 tablespoons flour
- ¾ teaspoon dry mustard
- ½ teaspoon garlic powder
- ½ teaspoon kosher salt
- ¼ teaspoon white pepper or regular black pepper
- 3 cups warm milk
FOR THE GRATIN:
- 1 small butternut squash peeled, seeded and thinly sliced
- 1 small rutabaga peeled and thinly sliced
- melted fennel and leeks from above
- bechamel from above
- 2 cups blend of grated cheese such as gruyere, comte, emmenthaler, mozzarella, monterey jack
PREHEAT THE OVEN:
- Arrange the oven rack in the center of the oven and Preheat the oven to 375° F.
FOR THE MELTED FENNEL AND LEEKS:
- Trim the leeks of the root and tough green ends. Cut the leeks into 1/4″ thick rounds and transfer to a medium bowl filled with cool water. Separate the leek rings and swish with the water to remove any grit or debris. Transfer to a salad spinner to dry the leeks.
- Heat the olive oil and butter over medium heat and add the leeks and fennel, salt, pepper and thyme.
- Stir to combine, cover with a tight fitting lid and reduce the heat to medium low, cooking until the vegetables are very soft, tender and translucent, about 10-12 minutes. Do not brown the vegetables. Set aside.
FOR THE BECHAMEL:
- In a large saucepan, melt the butter over medium high heat. Sprinkle in the flour, mustard powder, garlic powder, kosher salt and pepper. Whisk to combine, so that there’s no my dry floury bits.
- Add warm milk a little at a time, stirring constantly. It will be a little clumpy at first, but as you continue to stir (or whisk), the clumpier bits will melt into the sauce. Stir constantly and bring the sauce to a boil for one minute or until the bechamel sauce thickens. Set aside.
ASSEMBLE THE GRATIN:
- Spray a 2 quart casserole dish with vegetable spray. Spoon about 1/4 to 1/3 cup of bechamel sauce into the casserole and spread across the bottom.
- Layer the bottom with about 1/3 of the slices of rutabaga and butternut squash, alternating between the two to get a good blend.
- Top with 1/3 of the melted leeks, 1/3 of the bechamel and 1/3 of the cheese mixture.
- Continue layering the casserole like this, ending with bechamel and cheese. Cut a piece of tin foil to cover the dish and spray with vegetable spray. Cover the casserole tightly with the foil (vegetable spray side down) and bake for one hour. (The vegetable spray will prevent the cheese and topping from sticking to the foil.
- REDUCE THE OVEN TEMPERATURE TO 350° F.
- Remove the foil and continue to bake for 30 minutes or until the vegetables are tender and yield when poked with a sharp knife.
- Remove the gratin from the oven and let cool for 10 minutes before serving.
- Note: Rutabaga and butternut squash contain more liquids than you might think and will leak into the casserole. It doesn’t hurt anything, but if it bothers you, just tilt the casserole and spoon out the excess liquid (or use a turkey baster to suck it up). I soaked up about 1/3 cup of liquid from mine.
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