Preheat the oven to 400 degrees F. Line a 12-cup muffin tin with cupcake liners.
In a large bowl, whisk
the hot water and cocoa powder together.
In another large bowl, stir together brown rice
flour, sorghum flour, potato fl our, baking soda
, guar gum, and salt.
Add the sugar and butter to the cocoa mixture. With an electric mixer on high speed, beat until a smooth, shiny mixture forms, about 30 seconds. Then beat in the eggs and vanilla on low speed until incorporated.
Add half of the flour mixture and beat on low speed just until combined; there may be dry spots. Add 1/2 cup of the buttermilk, mixing on low speed until just incorporated. Repeat with the remaining flour mixture and the remaining buttermilk
. Fill each muffin cup to the top with the batter. Reserve the remaining batter and fill 4 more cupcake liners; set aside. Bake for 15 to 20 minutes, until the centers of the cupcakes are firm to the touch.
Remove the cupcakes from the muffin tin
and let them cool completely on a wire rack. Repeat with the remaining batter
Once the cupcakes are cool, use a small spatula
or a butter knife to ice them with your choice of icing. Store in an airtight container in the refrigerator for up to 5 days.