Begin by browning the sausage in a small quantity of vegetable oil over medium warmth. Utilizing a slotted spoon, switch cooked sausage to medium mixing bowl. Flip the pot to medium-high and add the sliced ​​mushrooms to the skillet. Sauté the mushrooms till they launch their moisture and start to brown.

Add child spinach to skillet and sauté till spinach is wilted. Add the mushroom and spinach combination to the bowl with the sausage and stir to mix. Put aside to chill barely.

In the meantime, whisk collectively 6 eggs, milk and Dijon mustard. Season egg combination with 2 teaspoons kosher salt and black pepper.

Add about 5 ounces (just a little greater than half) of the grated Fontina cheese to the sausage, mushrooms, and spinach combination and stir to mix.

Pour egg combination into sausage combination and stir to mix.

Frivolously grease a 12×9 casserole dish. Then tear 4 day-old croissants into greased plates.

Pour the egg, sausage, mushroom, spinach, cheese combination over the torn croissants. Use a spatula to unfold the combination evenly on the plate.

High with remaining grated fontina cheese. Then you’ll be able to sprinkle the cheese with sliced ​​inexperienced onions now, or you’ll be able to sprinkle the cheese with sliced ​​inexperienced onions after it comes out of the oven.

Cowl the casserole and refrigerate for no less than 8 hours or as much as in a single day.

When you find yourself able to bake, preheat the oven to 375° and permit the crust to return to room temperature whereas the oven preheats. Place the casserole on the pan and bake for about 1 hour, overlaying if essential to stop over-browning.

The strata is prepared when the middle feels barely agency and the highest is golden brown. Let the strata cool for about 10 minutes, then slice and serve.