Set your oven to 350°F (175°C). Grease and flour your cake pans or line them with parchment paper so the cake doesn’t stick. Set them aside.

In a large bowl, beat the butter (make sure it’s at room temp) and sugar together using a mixer. Keep mixing on medium-high speed until the mixture looks light and fluffy — this usually takes about 3 to 5 minutes.

Slowly add in the egg whites, mixing well after each addition. Once those are in, stir in the vanilla bean paste. The batter should be smooth and creamy.

In a separate bowl, sift together the flour, baking powder, and salt. Turn your mixer to low and add the dry ingredients in three parts, alternating with the sour cream. Start and end with the dry ingredients.

Pour in the oil slowly and mix just until everything is blended. Don’t overmix. Scrape down the sides of the bowl with a spatula to make sure nothing is stuck to the edges.

Divide the batter evenly into the pans. Bake for 30 to 35 minutes, or until a toothpick poked into the center of the cake comes out clean.

Once baked, take the cakes out of the oven and let them sit in the pans for about 10 minutes. Then gently remove them and place them on a wire rack to cool all the way.

In a heatproof bowl over simmering water, whisk egg whites, sugar, and a pinch of salt until the sugar dissolves and the mixture is warm. Transfer to a stand mixer and beat on high until stiff peaks form and the bowl is cool. Gradually add butter, then mix in vanilla bean paste. Beat until smooth and silky.

Once the cake layers are completely cool, trim the tops if needed so they’re flat. Stack the layers, spreading the frosting between each one. Then cover the top and sides with the rest of the frosting. Smooth it out with a spatula and decorate however you like.