Preheat the oven to 350F. Line with parchment paper and grease two 8-inch round cake pans with butter and dust with cocoa powder or gluten-free flour. Set aside.
In a medium bowl, add the gluten-free flour blend, xanthan gum (if using), cornstarch, cocoa powder, baking powder, baking soda, and salt. Whisk until all ingredients are combined.
Add granulated sugar and vegetable oil to a separate large mixing bowl. Beat with an electric mixer for a few minutes to combine.
Add in the eggs, vanilla extract, apple cider vinegar, red food coloring and stir to combine. Scrape down the sides of the bowl as needed.
Stir in the buttermilk and hot coffee.
Gradually add the dry ingredients, mixing until no more streaks of flour remain. Scrape the sides and the bottom of the bowl to ensure all of the dry mixture is incorporated. Let sit for 2-3 minutes to allow the batter to slightly thicken.
Divide the batter between the two prepared cake pans. I like to use a food scale to ensure that my layers have approximately the same amount of batter.
Bake at 350F for 35 to 40 minutes or until a wooden pick inserted in the center of the cake comes out clean.
Let cool completely on a wire rack. Level cakes if necessary, reserving any excess crumbs.