📖 Instructions

1. Preheat your oven to 350°F (175°C). Grease and flour three 8-inch cake pans. Alternatively, you can line the bottoms with parchment paper rounds for easy removal.
2. In a large mixing bowl, cream together 1 cup (2 sticks) of unsalted butter, softened, and 2 cups of granulated sugar until light and fluffy. This usually takes about 3-5 minutes with an electric mixer. Don't skimp on this step; it’s crucial for a tender cake!
3. Beat in 3 large eggs, one at a time, then stir in 1 teaspoon of vanilla extract. Make sure each egg is fully incorporated before adding the next.
4. In a separate bowl, whisk together 3 cups of all-purpose flour, 1 teaspoon of baking powder, 1/2 teaspoon of baking soda, and 1/4 teaspoon of salt. This ensures even distribution of leavening agents.
5. In a measuring cup, combine 1 1/2 cups of buttermilk and 1 tablespoon of white vinegar. Let it sit for a minute or two; it will look slightly curdled, but that’s perfectly fine!
6. Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk mixture, beginning and ending with the dry ingredients. Mix until just combined. Be careful not to overmix, as this can result in a tough cake. Think gentle folds, not aggressive stirring.
7. Divide the batter evenly among the prepared cake pans. I like to use a kitchen scale to ensure each pan has the same amount of batter for even layers.
8. Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean. Keep an eye on them after 25 minutes; ovens vary!
9. Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely. This prevents them from sticking and breaking.
10. While the cakes are cooling, prepare the Swiss meringue buttercream frosting. In a heatproof bowl set over a simmering pot of water (make sure the bottom of the bowl doesn’t touch the water), whisk together 6 large egg whites and 1 1/2 cups of granulated sugar until the sugar is completely dissolved and the mixture is warm to the touch. This step is crucial for a smooth frosting.
11. Remove the bowl from the heat and beat the egg white mixture with an electric mixer fitted with the whisk attachment, starting on low speed and gradually increasing to high speed, until stiff, glossy peaks form and the bowl is cool to the touch. This can take 8-10 minutes, so be patient.
12. Gradually add 1 1/2 cups (3 sticks) of unsalted butter, softened, one tablespoon at a time, beating well after each addition. The mixture may look curdled at first, but keep beating, and it will come together into a smooth, creamy frosting.
13. Stir in 1 teaspoon of vanilla extract.
14. Divide the frosting into three bowls. Tint one bowl with purple gel food coloring, one with pink, and one with blue. Use a light hand; you can always add more color, but you can’t take it away!
15. Once the cakes are completely cool, level the tops with a serrated knife if needed.
16. Place one cake layer on a cake stand or serving plate. Spread a generous layer of frosting on top. Repeat with the remaining cake layers and frosting.
17. Using a piping bag fitted with a large star tip, pipe swirls of purple, pink, and blue frosting around the cake. Get creative with your design! The goal is to create an ombre effect reminiscent of the Aurora Borealis.
18. Sprinkle edible glitter over the entire cake for a final touch of shimmer and magic.
19. Chill the cake for at least 30 minutes before serving to allow the frosting to set. This makes it easier to slice and serve.