Potato gratin, cheese enchilada casserole and spring onion pie are some vegetarian casserole ideas. Each of these casseroles incorporates cheese as a base ingredient and protein source.
To make Cooking Light's recipe for potato gratin, first preheat an oven to 375 degrees Fahrenheit. Rub an 11-by-7-inch baking dish with a clove of garlic, then coat the dish with butter. Pour 2 1/2 cups of whole milk into a skillet, then add 2 tablespoons of minced shallots, 1/4 teaspoon of kosher salt, 1/4 teaspoon of freshly ground black pepper, a dash of nutmeg and 2 pounds of peeled and sliced Yukon gold potatoes.
Bring the mixture to a simmer, and cook until the potatoes are almost tender. Spoon the potato mixture into the prepared baking sheet, and top with 1/2 cup shredded Gruyere cheese and 1/4 cup of grated Parmigiano-Reggiano cheese. Bake the casserole for 35 minutes, then broil for about 3 minutes or until the top of the dish is golden. Let the dish stand for 10 minutes before serving.
Southern Living's spring onion pie also uses Gruyere cheese; however, this recipe also incorporates flour, lending the casserole a more pastry-like texture. This recipe is baked in a cast-iron skillet rather than a baking dish.