Preparation of Oven and Baking Dish: Initiate the process by preheating the oven to a temperature of 375°F. Concurrently, prepare a 9×13-inch baking dish by applying a non-stick spray to its surface.

Cooking of Vidalia Onions: Place the Vidalia onions in a medium-sized saucepan and cover them with water. Elevate the temperature to high to bring the water to a boil. Once boiling, reduce the heat to allow the onions to simmer for approximately 8 minutes. Following this, drain the onions thoroughly and mix them with the unsalted butter.

Combining Eggs and Evaporated Milk: In a separate, larger bowl, whisk together the eggs and evaporated milk until the mixture is well combined. To this, add the cooked onions, Ritz cracker crumbs, grated cheddar cheese, salt, and black pepper. Stir the mixture until all ingredients are evenly distributed.

Assembly of Casserole: Carefully transfer the onion and egg mixture into the greased baking dish. In a separate container, blend the additional Ritz cracker crumbs with the melted butter, and then evenly distribute this mixture over the top of the casserole.

Baking Process: Insert the dish into the preheated oven and bake for 45 minutes, or until the center of the casserole is set and the surface has turned a golden brown color. The casserole is ready to be served upon completion of the baking process.