In a large bowl, cream butter and sugars together until it becomes pale. Add egg and milk, mix well. Add the starter, flour, baking powder, baking soda, spices and salt. Stir just until combined. Do not overmix the batter. Gently stir in the carrots, raisins and nuts, if using. Half fill your muffin cups with batter. Bake at for 20 to 25 minutes or until toothpick inserted in the center comes out clean.