In a large skillet heat 1 Tablespoon of the Onion (1) on medium-high heat. Add in your Olive Oil (1 tablespoon) and cook for 3-4 minutes until they become slightly translucent. Continue cooking and add your Cremini Mushroom (0.5 pound).
Cook for another 3-4 minutes and add 1 teaspoon of your Kosher Salt (1 teaspoon).
Next, add your Breakfast Sausage (0.5 pound) and allow the mixture to fully cook for another 4-5 minutes.
Meanwhile, heat your oven to 500 degrees F (260 degrees C) and prep your croissants to toast.
Slice each Croissants (8) in half and place them on a sheet pan. Drizzle lightly with the remaining Olive Oil (1 tablespoon), cut side up. You will probably need 2 sheet pans.
Toast slightly in the hot oven for only 2-3 minutes until croissants begin to brown. Remove and set aside.
In a large bowl, whisk your Egg (8), Whole Milk (2 cup), Heavy Cream (1 1/2 cup), Ground Black Pepper (1/2 teaspoon), Garlic Powder (1 teaspoon), Italian Seasoning (1 teaspoon), and 1 teaspoon of your Kosher Salt (1 teaspoon).
Butter or spray a 9x13 baking dish and place one layer of croissant (cut side up) in your baking dish, it’s okay to layer them. The bottom layer should have about 6 halves. Drizzle some of your sausage mixture and half of your Shredded Sharp Cheddar Cheese (1 cup).
Place another layer of croissants, be sure to fill in the center, you can tear croissants if needed. Add the rest of your sausage mixture and Shredded Sharp Cheddar Cheese (1 cup).
Carefully pour your egg mixture on top of the bake. Press the croissants slightly into the dish to coat.
Cover with foil and allow to sit in the fridge for at least 4 hours. It's better if you make it the night before.
Preheat the oven to 350 degrees F (180 degrees C).
Place the covered sheet pan in the oven and cook for 30 minutes.
Uncover and cook for an extra 10 minutes.
Remove from the oven. Top with Scallion (to taste) and a sprinkle of Everything Bagel Seasoning (to taste) if using. Enjoy warm or at room temperature.