01 - Preheat oven to 375°F. Grease an 8x8-inch baking dish with butter or nonstick spray and set aside.
02 - In a large, clean mixing bowl, beat the egg whites with an electric mixer on medium-high speed until stiff, glossy peaks form. Set aside.
03 - In a separate bowl, whisk together the egg yolks, cottage cheese, milk or cream, salt, black pepper, and sweet paprika until smooth and well combined.
04 - Fold the shredded cheddar, grated Gruyère or mozzarella, sliced green onions, and optional spinach or broccoli into the cottage cheese mixture until evenly distributed.
05 - Gently fold the stiffened egg whites into the cottage cheese mixture in two additions, using a spatula and light sweeping motions to preserve maximum volume.
06 - Pour the airy batter into the prepared baking dish and spread evenly, smoothing the top with a spatula.
07 - Bake on the center rack for 25 minutes, or until the top is golden brown and the center is just set. Avoid opening the oven door during baking.
08 - Remove from the oven and let rest for 5 minutes before slicing into portions. Serve warm alongside a fresh salad, roasted tomatoes, or crusty toast.