Sausage Mushroom Croissant Casserole

Name: Sausage Mushroom Croissant Casserole
Ingredients: 9 large croissants (torn in thirds); cooking spray; 1 lb ground sausage (plain or spicy); 2 tbsp Greek Freak spice blend (or other Italian Seasoning); 1 tbsp garlic powder; 1 tbsp olive oil; 8 oz mushrooms (quartered); 4 large eggs; ¾ cup milk; ¾ cup heavy cream; ½ cup shredded cheddar; ¾ cup shredded monterey jack; 1 pinch crushed red pepper flakes; kosher salt (to taste); black pepper (to taste); 3 tbsp butter (cut into small chunks); fresh thyme (leaves only, for garnish (optional))