Brush any dirt off the mushrooms using a soft vegetable brush or paper towel. Cut the mushrooms into bite-sized chunks. I cut one small chunk off the side roll the mushroom, continuing to lop off pieces as I go.
In a large skillet, heat 1 tablespoon olive oil over medium-high heat. Add 8 ounces mushrooms and cook until they release their liquid and begin to brown, stirring occasionally, about 5 minutes.
Add 3 tablespoons unsalted butter, 1 medium shallot & 2 large sage leaves to the mushrooms and sauté until softened, 2-3 minutes. Stir in ½ teaspoon kosher salt and ¼ teaspoon black pepper.
Sprinkle 2½ tablespoons flour over the mushrooms and stir until all the flour is absorbed and the mixture has a pasty look.
Stir in 1 tablespoon dry vermouth and simmer for one minute. Add 2 cups low sodium beef stock or bone broth slowly, stirring constantly.
Heat the gravy to a boil and continue to stir for one minute until the gravy thickens. Add 1 teaspoon Worcestershire sauce sauce and ½-1 teaspoon browning sauce, stirring until well combined.
Taste for seasonings and adjust as necessary, adding more salt or pepper if you like. Remove the mushroom sauce from the heat and pour into a gravy boat or bowl.
Notes
Each serving is about ¼ cup.
Leftovers can be kept for up to 5 days in an airtight container in the fridge.