Created by SugarPea on November 2, 2013
Step 1: Heat oven to 325 degrees.
Step 2: Butter a 9x9 inch baking pan.
Step 3: Sauté the onions, mushrooms and garlic in 3 tablespoon butter for 5 minutes. Blend in flour, salt, pepper and nutmeg. Gradually add half and half cream, stirring until thickened, then mix in 1/3 cup Parmesan cheese. Taste for seasoning then adjust if needed.
Step 4: In the buttered casserole, spread half the spinach; cover with the mushroom sauce, then top with remaining spinach.
Step 5: Sprinkle with the remaining 1/3 cup Parmesan cheese, then top with the grated gruyere cheese or Swiss cheese.
Step 6: Bake for around 40 minutes or until completely heated though.