Lightly butter the slow cooker then add bread cubes. In a small bowl, whisk together the scalded milk, eggs, sugar, cinnamon, nutmeg, salt, vanilla, and melted butter. Pour milk mixture over the bread cubes then add raisins, if desired. Gently, using a large spoon or spatula, press bread cubes down into mixture so all bread pieces will soak up milk mixture. Do not stir. Cover and cook on LOW setting for 5 to 6 hours, until bread pudding is set. Serve with a dessert sauce (links below) or whipped cream.