Preheat the oven to 350º F.
In a large bowl, add all dry ingredients and whisk to blend.
In a smaller bowl, add all wet ingredients and mix.
Pour the wet ingredients into the dry ingredients and mix until just barely mixed. If you overmix your batter, your cake will turn out dense. I never use a standing mixer when I make gluten free cake because I like my cakes to turn out fluffy.
Spray cake pans with coconut oil. Add batter to each layer pan. (*see note)
Bake for 20 minutes, checking to see if it is done. (Time cooking really will vary depending on pan size, or if you are making cupcakes.)
Remove from the oven. Tip the pans so cakes come out onto the cooling rack.
To test for doneness, insert a toothpick into the center of the cake. If the toothpick comes out clean, it is done baking. If you see batter or crumbs, the cake need to bake longer.
In a mixer, add frosting ingredients and mix until thick and creamy. (Start on low speed so powdered sugar doesn't fly all over your kitchen!)
When the cake is cool, frost each layer. Use a rubber spatula to smooth and spread the frosting all around the cake.