The essence of breakfast strata is eggs, milk, cheese, and bread. The personality comes from great fillings and this one is stuffed with mixed mushrooms, cheese, and spinach.
Grease a 12-muffin tin or an eight-inch by eight-inch cake pan with one tablespoon of butter and set aside.
Season and sautee the mushrooms on high heat or bake in an oven until the moisture is gone and they are reduced by half.
Heat one tablespoon of butter in a large pan on medium-high heat and add the onions herbs, and garlic and cook until soft add the spinach and cook until wilted. Set aside.
Meanwhile, whisk together the eggs, cream, and milk, add half the cheese, and mix in the cubed bread.
Mix the mushrooms in with the bread and cheese mixture and combine, add the mustard and the spinach onion mix and adjust the seasoning, let sit for 15 to 20 minutes.
Preheat oven to 375° F.
Add the mixture to the greased muffin tin or tray and bake in the preheated oven for 15 minutes or until the middle is cooked through.
When almost done remove from oven and top with remaining cheese. Return to the oven until the cheese has melted. Once melted, remove from oven and serve. Enjoy!