bread pudding recipe

6 cups day-old bread, cubed (such as French bread or challah) - 3 cups whole milk - 3/4 cup granulated sugar - 4 large eggs - 1 teaspoon vanilla extract - 1/2 teaspoon ground cinnamon - 1/4 teaspoon ground nutmeg - 1/4 teaspoon salt - 1/2 cup raisins (optional) - 2 tablespoons butter, melted