Grease and line 2 9-inch baking rounds with parchment paper.
In a medium bowl, whisk together the 3 cups gluten free flour, 1 tablespoon baking powder, and ½ teaspoon fine sea salt.
In a large bowl, beat the 1 cup unsalted butter and 2 cups granulated sugar together using an electric mixer until light and fluffy, about 5 minutes. Beat in the 4 large eggs one at a time, then add the 1 tablespoon pure vanilla extract.
With the mixer on low, add half the flour mixture to the butter and egg mixture and beat until just combined. Add the 1 ⅓ cups buttermilk and mix well to combine. Add the remaining flour mixture and beat until just combined, scraping down the bowl as necessary.
Preheat the oven to 350℉. Pour the batter into the prepared pans, and rest it while the oven heats. Then, place in the oven and bake for about 45 minutes, until a tester inserted in the middle of the cake comes out clean. Remove from the oven and place on a rack to cool for 20 minutes in the pan before turning out onto the rack to cool completely.
When ready, fill and frost the cake with your favorite frosting.
Notes
Tips
Use room temperature ingredients. Bring all of your ingredients to room temperature before mixing them together so that they blend in well.
Don't overmix. Mix the batter until just combined for the tenderest crumb (this is less important when using gluten-free flour, which doesn't have any gluten to activate, but it still helps).
DIY buttermilk. I believe that real buttermilk tastes the best! But, if you don't have it, mix 1 ½ cups of whole milk with 1 tablespoon + 1 teaspoon of vinegar, let it sit for 10 minutes, then measure out the amount you need to make the recipe.
To make it dairy-free: Mix 1 cup of non-dairy milk with 1 tablespoon of white vinegar, let it sit for 10 minutes, then measure it out to use in the cake. Swap the butter for a non-dairy butter.
What size? This recipe makes 2 9-inch cake rounds. You can also bake it as a sheet cake in a 9x13-inch pan, make 2 dozen cupcakes, or make 1 8 or 9-inch cake round and 1 dozen cupcakes.
Frosting Ideas
You can do any frosting you like on this cake! The photos show chocolate frosting - my fav - or you can try:
Whipped cream - Make homemade whipped cream and top the cake with a thick layer of lightly sweetened cream and berries.
Ice cream cake - Use your favorite ice cream and use the cake to make a homemade ice cream cake.