Make the streusel by mixing the sugar, brown sugar, walnuts, vanilla, and cinnamon together in a small bowl. Set it aside.

Preheat the oven to 350 degrees F. Generously brush a round 9 by 2-inch deep cake pan with butter. In a medium bowl whisk the flour, baking soda, salt, nutmeg and mace together and set it aside.

In a standing mixer fitted with the paddle attachment, or with an electric hand-held mixer, cream the butter and sugar on medium speed until light and fluffy. Add the eggs, one at a time, mixing until incorporated. Mix the vanilla with the sour cream. Add the flour mixture in 3 parts to the butter mixture, alternating with the sour cream in 2 parts until just combined.