Preheat the oven to 350 degrees F (175 degrees C).
Place bread pieces into an 8-inch square baking pan. Drizzle melted butter over bread and sprinkle raisins over top.
Whisk milk, sugar, eggs, cinnamon, and vanilla together in a medium mixing bowl until well combined. Pour mixture over bread, and lightly push down with a fork until all bread is covered and soaking up the liquid.
Bake in the preheated oven until golden brown and the top springs back when lightly pressed, about 45 minutes.