Preheat oven to 350 degrees F. Spray 6 or 8-cup tube or bundt cake pan with cooking spray. Set aside.
Sift flours, cocoa, xanthan gum, baking soda, baking powder, and salt in a bowl. In another small bowl combine coffee, prunes, vanilla and milk.
In large bowl, use electric mixer to beat butter, eggs, sugar and orange peel for four minutes at thigh speed. At low speed add flour mixture alternately with milk/prune mixture in three separate additions. Continually scrape edges of bowl.
Place batter in prepared pan and bake 40 minutes, or until toothpick inserted into center comes out clean. Remove from oven and cool on rack for 10 minutes. Turn cake onto serving plate. Cool completely.