Preheat the oven to 350°F. Line a muffin tin (or two) with 12 liners.
Whisk the oat flour, millet flour, brown rice flour, sweet rice flour, tapioca starch, xanthan gum, cocoa powder, sugar, baking soda, baking powder, and salt together in a medium bowl.
In a separate bowl, whisk the buttermilk, egg, oil, vanilla extract, and chocolate extract together until smooth. Pour this mixture into the dry ingredients and stir lightly.
Pour the hot water into the dry ingredients and mix until completely smooth, scraping up the sides and bottom to completely incorporate.
Use an ice cream scoop to divide the batter among the 12 lined cupcake cups, filling no more than half full (these cupcakes rise quite a bit)
Bake for about 22 minutes, or until a toothpick inserted in the center comes out clean or with just a few moist crumbs.
While the cupcakes bake, prepare the filling and frosting.
Transfer the cupcakes to a wire rack to cool.
Once the cupcakes are cool, use a small round cutter or the back of a pastry tip to punch out a hole in the center of each cupcake and fill with jam.
Pipe chocolate buttercream over the top and serve. (Optional: garnish with currants)
Raspberry Currant Filling
In a small bowl, mix the raspberry jam and currant jelly together until smooth.
Chocolate Buttercream
Sift the cocoa powder and powdered sugar together and set aside.
In the bowl of a stand mixer, beat the butter until light and fluffy.
Add the cocoa/sugar mixture to the butter, alternating with the milk and beating until smooth.
Add the extract and mix until light and fluffy. If the buttercream is too soft, you can either add a tablespoon of more sugar, or continue beating while holding an ice pack against the bowl to chill it a bit.
Notes
*I grind my own oat flour by pulsing gluten-free oats in the blender or food processor until fine, then sifting out any large pieces.**For non-gluten-free version, replace the oat flour, millet flour, brown rice flour, sweet rice flour, tapioca starch, and xanthan gum with ¾ cups all-purpose flour
This nutritional information has been automatically calculated, and as such, may be incomplete or inaccurate. Please reference the specific ingredients you use for the most accurate nutritional information.