Preheat oven to 350. Combine dry ingredients. Add butter, milk, and vanilla. Beat one minute on medium speed. Add each egg one at a time, beating after each addition for one minute. Beat on high for one minute. Spoon batter into cup cake liners in muffin pan (2/3 full). Bake 20 - 25 minutes. Cool in pan for 5 minutes and then remove and place on wire rack.