Preheat oven to 350 degrees F (175 degrees C). Spray an 8×11 inch casserole with nonstick spray.
In a large bowl, combine bread cubes, 1 cup sugar, salt, cinnamon, and nutmeg. Mix in raisins, if desired.
In another bowl, blend milk, melted butter, and eggs. Add wet ingredients to dry, and mix together without turning bread mixture into mush. Pour mixture into prepared casserole dish.
Place casserole dish into a larger baking pan. Pour hot water into baking pan about 1/3 up the side of the casserole dish, creating a water bath. Bake for 45 minutes.
In a small saucepan, combine 1/2 cup sugar, cornstarch, 1 cup hot water, 2 tablespoons butter, lemon juice, and lemon zest. Cook on medium heat until bubbling and thickened. Stir constantly to avoid scorching. Serve with bread pudding.