"A new version of French toast casserole. I had some left over cinnamon rolls that had become stale and still wanted to use them so I came up with this recipe and it was a huge hit at my Sunday brunch."
Slice cinnamon rolls into 1-inch squares. Whisk milk, eggs, vanilla extract, and cinnamon together in a bowl.
Slice 1 banana and layer on bottom of a 9x13-inch baking dish; top with brown sugar. Layer cinnamon roll squares on top of banana. Pour egg mixture over cinnamon rolls; press cinnamon rolls with a spatula to allow egg mixture to fully coat. Cover with aluminum foil and refrigerate until egg mixture is absorbed, 1 hour to overnight.
Preheat oven to 375 degrees F (190 degrees C).
Bake in preheated oven until firm, about 50 minutes. Remove aluminum foil and bake until golden brown, about 10 minutes more. Remove from oven and let stand for 10 minutes. Slice remaining banana and place on top to serve.