In a small bowl, combine the nuts, brown sugar and cinnamon; set aside.
Preheat oven to 350°.
In a standing mixer fitted with a paddle, cream butter, sugar and zest until light and fluffy. (Alternatively, place ingredients in a large bowl and use a hand mixer.)
Add eggs 1 at a time, beating well after each addition. Beat in vanilla.
Combine the flour, xanthan gum, baking powder, baking soda, salt and spices.
Add 1/2 cup flour mixture to the creamed ingredients, mix on low until just blended. Add 1/3 cup sour cream, mix on low until just blended. Repeat steps, ending with flour.
Pour 1/2 batter into a greased 10-inch Bundt pan. Smooth batter evenly with back of a spoon. Sprinkle with 1/2 of the streusel topping mixture, stopping before the edges, and swirl it in with a knife tip.
Repeat with remaining batter and streusel topping mixture.
Bake 45 to 60 minutes, or until a toothpick inserted near the center comes out clean.
Cool for 3 to 5 minutes before removing from pan onto a cake plate. Dust with powdered sugar. Serve with "The Best Cranberry Sauce"*.
Editor's note: The cake has a mild spice flavor. For more pronounced spice notes, increase the amount of spices called for in the recipe.
This recipe comes courtesy of Katherine Glassman of Sticky Fingers Baking Company in Ventura.