Preheat the oven to 175°C (350°F) and grease a baking dish with butter.
Tear day-old bread into small pieces and place them in the dish. Drizzle melted butter over the bread.
Sprinkle raisins evenly over the bread (optional).
In a bowl, whisk together milk, eggs, sugar, cinnamon, and vanilla until well combined.
Pour the mixture evenly over the bread and let it soak for 5 minutes.
Bake for 45 minutes or until the top is golden brown and a knife inserted comes out clean.
Let it cool slightly before serving. Serve warm with a drizzle of caramel or a scoop of vanilla ice cream.