Preheat the oven to 400°. Line a roasting pan with tin foil or parchment and place the whole bell pepper in the center. Cook for 25-30 minutes in the hot oven until the skin has blackened and is puffed and the flesh is tender. Transfer the pepper to a small bowl and cover tightly with plastic wrap. Cool the pepper to room temperature.
Peel off the skins and remove the stem and seeds. Chop the pepper into 1/2" pieces and set aside.
PREPARE THE BREAD BOWL:
Use a sharp serrated knife to cut off the top of the sourdough bread, leaving an opening that slightly curves back into itself. Scoop out the stale bread, leaving about 3/4" still attached to the crust throughout the loaf. (save the interior for breadcrumbs or stuffing). Set the bread bowl aside.
In a large skillet over medium high heat, add the olive oil. When the oil is hot add the mushrooms and saute until browned and have given up most of their liquid. Transfer mushrooms to a medium bowl.
Add the ground pork sausage to the pan and saute, breaking the sausage apart into small chunks and browning it. Transfer the sausage to a mesh strainer to remove as much liquid as possible.
Turn the heat off the pan and add the spinach to the pan along with the hot drained sausage. Toss until the spinach wilts.
Drain any excess liquid from the mushrooms and add them to the pan with the spinach and sausage.
Use a paper towel to remove excess moisture from the roasted bell pepper and add to the sausage mixture. Toss to combine.
Transfer the sausage mixture to the hollowed out loaf of bread and set aside.
MAKE THE CUSTARD:
In a medium bowl combine the eggs, cream, pepper, salt, oregano, marjoram, basil and cayenne pepper and whisk to combine.
Transfer the sausage filled bread boat to a sheet pan, lined with parchment paper or tin foil (sprayed with vegetable spray)
Pour about half of the custard over the sausage mixture and let it rest for 10-15 minutes or until it's soaked into the bread. Add another cup of the custard mixture and lightly cover the stuffed bread with plastic wrap. Refrigerate for 2 hours or overnight. Cover the remaining custard mixture and refrigerate.
TO BAKE THE BREAD CASSEROLE
When you're ready to bake, remove the bread from the refrigerator about half an hour before baking to take the chill off the casserole.
Preheat the oven to 350°.
Pour the remaining custard over the bread casserole. Sprinkle with cheese. Tent the bread with tin foil and bake for 40 minutes. Remove the foil and continue baking for Bake for 20-30 minutes more or until the eggs are set.
Remove the bread casserole from the oven and let it rest for 10 minutes before cutting.
To serve, use a sharp serrated knife to cut crosswise pieces about 1 1/2" thick and transfer to a plate.