Preheat oven to 350 degrees. In medium bowl, mix buttermilk, oil, applesauce, and egg with fork until blended. Stir flours, brown sugar, cocoas (can use all regular cocoa, they just won't be as dark), baking soda, salt, and xantham gum together. Add vanilla, flour mixture, and chocolate chips to wet ingredients. Stir together until just blended.
Divide batter evenly among 12-14 large muffin cups.
Bake 20-25 minutes or until tooth pick inserted in center comes out clean. Cool 5 minutes; remove from pan. Serve warm or cool.
* I like to use Domato Flour for my GF flour mixture, but you can use any GF flour mixture and I sometimes substitute Montina All Purpose Baking Flour for the Teff Flour. I make my oat flour by blending gluten free oats in the blender.
(.2/9/18 update, if using a flour blend that does not contain xanthum gum, add 1/4 teaspoon to the flour mixture).