Mix dry ingredients in a bowl, set aside. In another bowl whisk together the eggs with the buttermilk. Add mashed sweet potatoes or yams.
Mix in dry ingredients slowly, mixing together. Then add melted butter and incorporate into a batter that is smooth.
Preheat oven to 375 degrees F. Spray inside of a 9x9" pan with non stick spray and pour in batter. Bake for about 35 minutes or until toothpick in center comes out mostly clean with moist crumbs attached, no longer.
Cool for 5 minutes, slice and enjoy with butter on top of slice.