Grease the sides of two 9-inch cake layer pans. Trace around the bottom of pans onto a sheet of parchment paper. Cut them out and place them inside the bottoms of your pans.
In a medium mixing bowl, whisk together the rice flour, tapioca flour, potato starch, baking, powder, xanthan gum, and sea salt.
In a large bowl (Use a stand mixer, if you have one.), beat the butter until light. One by one, add the sugar, eggs, coconut milk, avocado oil, and vanilla. Continue beating until the batter is smooth.
Pour batter into prepared pans. Bake for 25 minutes.
Allow cake to cool on a wire rack for 10 minutes. Remove cake from pans, and let it finish cooling.
Fill and decorate this cake as you wish. It's good with jam between the layers and whipped cream and fresh berries on top!