Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 2-quart baking dish.
Mix bread and butter together in a bowl until evenly combined. Whisk sugar, eggs, and milk together in a separate bowl until smooth. Add bread mixture and pineapple to sugar mixture; stir well. Pour bread-pineapple mixture into the prepared baking dish.
Bake in the preheated oven until bubbling and lightly browned, about 1 hour.