Grease the sides of two 9-inch (23 cm) 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 flours, 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 and eggs. Combine the coconut milk, avocado oil, and vanilla in a measuring cup. Add the dry, flour mixture to the batter in 3 parts, alternating with the liquid mixture in 2 parts. Continue beating until the batter is smooth.
Pour batter into prepared pans. Bake for 25 minutes in preheated oven, until the internal temperature reaches 210°F (99° C).
Allow cake to cool on a wire rack for 10 minutes. Remove cake from pans, and let it finish cooling.
Decorate as you wish.
Fill and decorate this cake as you wish. It's good with jam between the layers and whipped cream and fresh berries on top!