Put oven rack in middle position and preheat oven to 350°F. Grease cake pans or line cupcake pan with liners. In a large bowl, mix coconut flour, baking powder, salt, and spices. In another bowl (or food processor), beat together butter and sweetener with an electric mixer at medium-high speed until pale and fluffy, 3 to 5 minutes. Beat in eggs 1 at a time, beating well after each addition, then beat in sour cream and vanilla. Reduce speed to low, then add coconut flour mixture and blend until batter is just smooth. Spoon batter evenly into pans (or cupcake liners) to about 2/3 full. Bake until pale golden and a wooden pick inserted in center of cakes comes out clean, 30 to 35 minutes. Cool 10 minutes in pans on racks. Run a thin knife around edge of pans, then invert racks over pans and reinvert cakes onto racks to cool completely.