Preheat oven 325 degrees. Grease and flour two regular loaf pans or 4 small.
In a stand mixer with the whip attachment, cream together the butter and sugar until light and fluffy. Use a medium speed (about 6)
Add eggs one at a time. Beat well after each addition and scrape down sides and bottom the bowl with a spatula as needed. Use a low to medium speed (about 4)
In a medium bowl mix together cake flour, mace and cream of tartar. If you have a sifter, sift this mixture 3 times. If not just use a fork or whisk to make sure the mixture is light, without any clumps.
Add sifted flour mixture on low speed (about 1). Mix just until all the flour disappears.
Pour cake batter into prepared pans (well greased and floured!). Bake for 1 hour to 1 hour and 15 minutes, depending on the size of loaves you're baking. Let cool completely before removing from pan. Loosen the edges with a knife and invert loaf pan to remove the cake.
Serve with coffee or whipped cream and berries.
Mace is a spice made from the lacy, red outer coating that covers the shell around the nutmeg kernel. It adds a delicate sweet-spicy flavor. If you can't find it at the store, you may use nutmeg in half the amount, as nutmeg is more potent.