Heat oven to 350 degrees F. Grease two 8-1/2 x 4-1/2 x 2-5/8-inch loaf pans. Dust with all-purpose flour; tap out the excess flour.
Stir together flour, baking powder, cinnamon, baking soda, salt, nutmeg and mace in medium-size bowl.
Beat together softened butter and granulated and light-brown sugars in large bowl until light and fluffy. Beat in mashed sweet potato until light and fluffy. Add eggs, one at a time, beating well after each addition. On low speed, beat in flour mixture in 3 additions. Beat in vanilla. Spoon batter into prepared pans, dividing equally; smooth tops with a rubber spatula.
Bake in 350 degree F oven for 55 minutes or until wooden pick inserted in centers of poundcakes comes out clean. Cool cakes in pans on wire rack for 3 minutes. Invert pans; remove pans and place cakes, right side up, on wire racks to cool completely. Slice and dollup with whipped cream if desired. Store cakes, well wrapped, at room temperature, or freeze. Thaw frozen pound cake overnight in the refrigerator. Makes 2 loaves.