Cream butter and sugar on medium speed for 3 minutes. Add eggs and sweet potatoes/yams and mix another 3 minutes.
In a separate bowl, whisk dry ingredients until well combined. Pour dry ingredients into the wet and mix on low until combined.
Spoon batter into well-greased muffin tins and fill 3/4 of the way. Bake at 350 degrees for 25 minutes or until golden brown and a toothpick comes out clean.