Preheat your oven to 350°F (175°C). Grease the 9x9-inch baking dish with butter.
In a large mixing bowl, combine the milk, sugar, eggs, vanilla extract, cinnamon, and salt. Whisk together until well incorporated.
Add the cubed bread to the mixture. Stir gently to ensure all the bread is soaked. If desired, fold in the raisins.
Pour the bread mixture into the prepared baking dish, spreading it evenly.
Bake in the preheated oven for 45 minutes, or until the top is golden brown and a knife inserted into the center comes out clean.
Remove from the oven and let it cool for a few minutes before serving.
Serve warm or at room temperature. Optionally, pair with vanilla ice cream or a drizzle of caramel sauce.