Step 1
Place the bun tops top down in a buttered 13- x 9-inch casserole dish. Set aside the bun bottoms.
Step 2
In a large skillet melt butter over medium-high heat until sizzling.
Step 3
Add onion and saute until they're just softening. Add mushroom slices and stir reducing heat to medium. Cook for about 5 minutes.
Step 4
Stir in herbs garlic paprika and salt and pepper to taste then add spinach and cook another 3 minutes stirring to wilt the spinach. Remove from heat.
Step 5
Spoon half the vegetable mixture evenly over the bun tops in the casserole dish. Scatter half the bacon and cheese evenly on top.
Step 6
Place the bun bottoms with cut side up in the casserole to form the top layer.
Step 7
Spoon the rest of the vegetable mixture bacon and cheese over the top layer of buns.
Step 8
In a bowl stir together eggs and milk until blended.
Step 9
Pour the mixture evenly over the casserole. Using a spatula press down firmly on each of the buns to submerge in the liquid. Cover tightly with plastic wrap and refrigerate 8 hours or overnight.
Step 9
In the morning let casserole sit at room temperature for about 30 minutes.