Preheat the oven to 350°F. Line a standard muffin tin with 12 liners.
Combine the milk and vinegar in a small cup and let sit while you measure the flour, at least 5 minutes.
Whisk the sweet rice flour, oat flour, millet flour, cocoa powder, sugar, baking powder, baking soda, and salt together in a medium bowl.
In a separate bowl, whisk the milk and vinegar mixture with the egg, oil, vanilla extract, and chocolate extract together until combined. Pour this mixture into the dry ingredients and stir lightly to combine.
Pour the hot water into the dry ingredients and mix until completely smooth, scraping up the sides and bottom to completely incorporate.
Divide the batter evenly among the prepared cupcake liners, filling them just over halfway, or with just less than ¼ cup of batter using an ice cream scoop.
Bake for about 20-24 minutes, or until a toothpick inserted in the center of one comes out clean or with just a few moist crumbs and the center bounces back when poked. In my experience, it's best to err on the side of an extra minute or two to be sure. This cake is very moist so it won't over bake very easily!
Let cool completely before frosting.
Meanwhile prepare the frosting.
Strawberry Hibiscus Frosting
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter over medium speed.
With the mixer on low, slowly add the powdered sugar, ground freeze-dried strawberries, vanilla extract, and rose water, if using. Beat until combined.
Add the heavy cream, 1 tablespoon at a time to loosen until soft enough to pipe, but still sturdy.
Fill a piping bag fitted with a ½-inch closed star pastry tip (I use Ateco 846) with the frosting. Pipe your roses onto your cupcakes, starting in the center and tapering off on the final time around. Decorate with dried rose petals, if desired.
Notes
*I use homemade oat flour by grinding gluten-free rolled oats in my blender or food processor until fine.**I divide my batter equally among 12 standard cupcake liners, filling them just above half full, which bakes up 12 perfectly-sized cupcakes that just reach the brim of the liner. One friend said she filled them higher and had just a little muffin top, but got only about 8 cupcakes.While trying to recreate her results, I discovered that there is a small difference in cupcakes baked with store-bought gluten-free oat flour versus those baked with home-ground gluten-free oat flour, where the store-bought oat flour cupcakes rose just ever so slightly less, but still made a bangin' cupcake. If you're using store-bought oat flour, I recommend making 11 cupcakes.
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.