First, I’d preheat the oven to 350°F (175°C). While that’s warming up, I’d grease two 9-inch round cake pans really well, line the bottoms with parchment paper, and give them a light dusting of flour. That way, the cakes won’t stick when it’s time to remove them.

In a big bowl, I’d whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt. I like to make sure it’s evenly mixed so there are no clumps this helps the cake rise evenly.

In another bowl, I’d beat the eggs, egg yolk, vegetable oil, buttermilk, warm water, and vanilla extract until everything is smooth and blended together.

I’d slowly pour the wet mixture into the dry ingredients. Then I’d fold everything gently with a spatula or whisk, just until it’s combined. I try not to over mix because that can make the cake dense instead of light and fluffy.

I’d divide the batter evenly between the two pans and smooth the tops so they bake evenly.

I’d pop them in the oven for 35–40 minutes. I usually check at 35 minutes with a toothpick; if it comes out clean, it’s done. Once baked, I’d let them cool in the pans for about 10 minutes.

After that, I’d carefully lift the cakes out and place them on a cooling rack to cool completely before frosting. You don’t want warm cakes or the frosting will melt.

For the white icing, I’d beat butter until creamy. Then I’d slowly add powdered sugar, a cup at a time, alternating with a little milk, and keep beating until it’s fluffy and smooth. A splash of vanilla goes in at the end.

I’d place one cake layer on a plate or cake board and spread a thick, even layer of icing on top. Then the second layer goes on, and I’d cover the top and sides with the rest of the frosting.

Finally, I’d decorate it however I like maybe sprinkles, chocolate shavings, or fruit and let it chill for 15–20 minutes to set the frosting. Then it’s ready to slice and enjoy!