Preheat oven to 400°F. Line muffin tins with paper liners, or spray with gluten free cooking spray.
Mix, cocoa powder, flour, sugar, baking soda, baking powder, salt, and xanthan gum in a large bowl with a whisk. Add eggs, buttermilk, hot water, canola oil and vanilla extract and beat well until thoroughly combined.
Spoon dough into prepared muffin tins, filling each cup about ⅔ full. Bake for about 20-25 minutes, or until a toothpick inserted in the middle of the cupcake comes out clean. Let cool in the pan for 5 minutes, then remove to a cooling rack to finish cooling completely.
Make the frosting. Beat the butter with the powdered sugar, milk, extracts and salt until light and fluffy. Frost as desired when cupcakes have cooled.