Cake:
Preheat oven to 350°F (175°C). Line your baking pan with parchment paper.
In a large bowl, whisk together the almond flour, coconut flour, tapioca flour, baking powder, baking soda, and salt. Set aside.
In another bowl, cream together the softened butter and sweetener until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.
Alternately add the dry ingredients and almond milk to the wet ingredients, mixing until just combined. Do not overmix.
Pour the batter into the prepared pan and smooth the top.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool completely in the pan before frosting.
Frosting:
In a large bowl, beat together the softened butter and powdered sweetener until light and fluffy.
Add the almond milk and vanilla extract, and beat until smooth and creamy.
Once the cake has cooled, spread the frosting on top and decorate as desired.