Purchase your Colomba HERE.
Preheat oven to 350 degrees F (175 degrees C).
Slice Colomba into small cubes. Place in an 8 inch square baking pan. Drizzle melted butter over Colomba. If desired, sprinkle with raisins.
In a medium mixing bowl, combine eggs, milk, sugar, and vanilla. Beat until well mixed. Pour over bread, and lightly push down with a fork until bread is covered and soaking up the egg mixture.
Bake in the preheated oven for 50 minutes, or until the top springs back when tapped.