1. Preheat over to 350 degrees Fahrenheit. Butter an 8-inch round cake pan. Line the bottom of the cake pan with wax paper and butter the paper. Lightly flour the pan, being sure to tap out any excess flour.
2. Beat butter with brown sugar, lemon zest, vanilla, baking powder, and salt. Beat until light and fluffy. Add egg yolks one at a time, beating well each time.
3. Combine ground almonds and flour and stir into egg mix. Stir in lemon juice. Whip egg whites with cream of tartar to soft peaks. Fold the egg whites into batter in 3 additions.
4. Spoon batter into prepared cake pan and bake approximately 35 to 40 minutes or until a pale goldish color and toothpick comes out clean. Let cool on rack for 15 minutes. Remove cake from pan and peel off paper. Let the cake completely on a wire rack. Transfer cake to a platter and dust with confectioners' sugar (if desired).
Yield: 8 servings
Fat: 16.5g (6.5g saturated fat)