The Best Breakfast Strata

Name: The Best Breakfast Strata
Ingredients: 8 plain croissants (about 1 1/4 pounds), split in half; 8 ounces sliced bacon, cut into 1/2-inch pieces; 12 ounces cremini mushrooms, thinly sliced; Kosher salt and freshly ground black pepper; 12 small or 8 large scallions, thinly sliced, white and dark green parts separated (about 1 cup whites and 1 1/3 cups greens); 12 ounces fontina cheese, shredded on the large holes of a box grater (about 3 cups); 2 cups heavy cream; 2 cups whole milk; 2 teaspoons Dijon mustard; 1 1/2 teaspoons paprika; 10 large eggs; Unsalted butter or nonstick cooking spray, for the baking dish; 2 tablespoons grated Parmesan