Preheat oven to 350°F and grease and lightly flour a 9 × 13-inch cake pan or line 12 cupcake tins with paper liners.
In medium bowl, combine sorghum flour, cocoa powder, potato starch, buckwheat flour, sweet white rice flour, xanthan gum, baking soda, baking powder, and salt. Whisk well to make sure everything is completely combined.
In large mixing bowl, combine the olive oil, sugar, and tahini. Add one- third of the flour mix and stir until well combined. Mix in the coffee and coconut milk and the remaining flour mixture a little at a time until all has been incorporated. Stir in the vinegar until the batter is smooth and fluffy.
Spread the cake batter into a prepared cake pan, or drop about ½ cup of batter into each cupcake liner. Bake for 27 to 30 minutes for sheet cake or cupcakes, or until knife inserted into the middle of the cake comes out clean. Let cool completely before frosting. Store covered for up to 3 days.