Preheat your oven to 350°F (175°C) and prepare three 8×2-inch round cake pans by greasing and flouring them.

In a medium mixing bowl, whisk together the gluten-free flour, baking powder, baking soda, and salt for 30 seconds to evenly distribute the leavening agents. Set this mixture aside.

In a separate bowl, combine the buttermilk, vegetable oil, and vanilla extract, stirring until well mixed. Set aside for later.

In the bowl of a stand mixer, beat the softened butter at medium speed until it’s smooth and creamy. Gradually add the sugar, continuing to mix on medium speed for 3 to 5 minutes, or until the mixture becomes light in color and fluffy.

Add the eggs one at a time, mixing just until each yolk is fully incorporated before adding the next.

With the mixer on low, alternate adding the flour mixture and the buttermilk mixture, beginning and ending with the dry ingredients. Add the dry mixture in three parts and the liquid in two. Mix only until the batter is just combined after each addition to avoid over-mixing.

Divide the batter evenly among the three prepared pans and smooth the tops with a spatula.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center of each cake comes out clean or with just a few crumbs attached. Allow the cakes to cool in their pans for 10 minutes before turning them out onto a wire rack to cool completely.

Beat the slightly softened butter until smooth and creamy. Add the vanilla extract and blend until combined.

Gradually add half of the confectioners’ sugar and most of the milk. Beat on medium speed until the mixture is smooth and the sugar is fully incorporated.

Add the remaining sugar and milk, and continue mixing at medium speed for another 3 to 4 minutes, scraping down the sides of the bowl as needed. For a smooth, air-free buttercream, reduce the mixer speed to low (setting #2 on a Kitchenaid) and beat for an additional 1 to 2 minutes.

This recipe yields approximately 4 ½ cups of buttercream, enough to generously frost a two-layer 8 or 9-inch cake. The buttercream can be stored in an airtight container and frozen for up to three months; thaw at room temperature before using.

Adjust consistency as needed: if the buttercream is too thin, add more sugar; if too thick, add a touch more milk.