Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter or non-stick spray.
Prepare the cinnamon rolls: Open the cans of cinnamon rolls and cut each roll into quarters. Arrange them evenly in the prepared baking dish.
Make the custard mixture: In a large mixing bowl, whisk together the eggs, milk, brown sugar, vanilla extract, and melted butter until fully combined.
Pour the custard mixture: Pour the egg mixture over the cinnamon rolls, ensuring all pieces are soaked evenly. Use a spoon to gently press the cinnamon rolls into the mixture.
Bake: Place the casserole in the preheated oven and bake for 30-35 minutes, or until the top is golden brown and the casserole is set in the center.
Frost the casserole: Once out of the oven, drizzle the frosting from the cinnamon roll package over the top, or use your favorite frosting (cream cheese or maple glaze works great!).
Serve: Allow the casserole to cool for 5-10 minutes before serving. Enjoy warm!