Step 1

Grease a 9x12-inch baking dish.

Step 2

Stir 1 cup brown sugar and butter together in a saucepan over medium-low heat until butter melts and sugar dissolves into butter, 2 to 4 minutes. Pour into prepared baking dish and spread a 1 1/2- to 2-inch layer of bread pieces over the top.

Step 3

Beat milk, eggs, and vanilla extract together in a bowl; pour milk mixture over bread into the baking dish and move bread as necessary to ensure all bread is absorbing liquid. Sprinkle cinnamon over the top. Cover the dish with plastic wrap and refrigerate, 8 hours to overnight.

Step 4

Preheat oven to 450 degrees F (230 degrees C). Remove and discard plastic wrap from baking dish and sprinkle remaining brown sugar over the top of the bread mixture.

Step 5

Bake in the preheated oven until browned and bubbling, about 30 minutes.