To prepare a tuna mornay casserole pasta bake recipe, you will first need to prepare the ingredients for the casserole. You will need: 2 tblsp. butter, 2 tablespoons kosher salt, 1 tablespoon thyme sprigs, 1/2 teaspoon paprika, 1/4 teaspoon cayenne pepper, and 1 teaspoon pepper. Toss the pasta with the butter and salt and pepper to taste. Pour the mixture into the prepared casserole dish and bake in the preheated oven for 30 minutes or until the top is golden brown. Remove from the oven and sprinkle with shredded Parmesan cheese.