Preheat the oven to 350°F. Prepare three 6-inch cake pans or 2 8-inch cake pans by lightly oiling them, lining them with a round of parchment paper, then lightly oiling and dusting the bottom and sides with oat flour. Or, for cupcakes, line a muffin tin with 24 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 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.

Divide the batter among the 3 prepared cake pans and smooth the tops. (Or cupcake liners)

Bake for about 33-37 minutes, or until a toothpick inserted in the center 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! (For cupcakes bake for 18-22 min)

Let cool in the pans for 5-10 minutes, then overturn the cakes onto wire racks to cool completely.

Meanwhile prepare the frosting.

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter over medium speed.

Add the cream cheese and beat until completely smooth.

Slowly add the powdered sugar, in thirds, mixing on low speed until combined.

Add the vanilla and salt, and beat on medium speed until smooth.

For a purely pink cake, add the hibiscus powder and beat until smooth. For an ombre cake like the one shown here, divide the frosting into four bowls and add the hibiscus and beet powder as follows: Dark Pink: ¾ cup frosting + ¾ teaspoon beet powder + ½ teaspoon hibiscus powder - Medium Pink 1½ cups frosting + 1 tablespoon hibiscus powder - Light Pink: ¾ cup frosting + ¾ teaspoon hibiscus powder - White: 2 cups frosting + ½ teaspoon hibiscus powder

To frost the cake, place one cake layer on the cake stand, spread ⅓ cup frosting (medium pink if making ombre) in an even layer. Place the second cake layer over the top and spread another ⅓ cup frosting (light pink if making ombre). Use the white frosting to create a very thin crumb coat layer and chill for 10 minutes. Frost the whole cake, smoothing with an offset spatula. For ombre, pipe 1-2 large rings of each color of frosting around the cake, as shown, finishing with white frosting on top. Smooth with an offset spatula, wiping after each use. Enjoy!