On medium speed, cream butter until smooth. Add Splenda gradually, beating until fluffy; about 3 minutes. Gradually add eggs one at a time, beating between additions. Add the dry ingredients in three parts. Alternate adding dry ingredients with the milk and vanilla. Blend well with each addition, but do not overbeat. Using a rubber spatula, scrape the batter from the sides of the bowl. Spoon the batter into cupcake liners, filling them 3/4 full. Bake for 20 to 25 minutes