Preheat your oven to 350°F (175°C). Grease and flour three 8 inch round cake pans, and line the bottoms with parchment paper. Properly preparing your pans ensures your cake won’t stick and will release easily once baked.

In a large mixing bowl, whisk together the cake flour, baking powder, and salt. This step helps evenly distribute the leavening agents, so your cake rises beautifully.

Using a stand mixer with a paddle attachment, beat the butter on medium speed until creamy, about 1 minute. Gradually add the granulated sugar and continue beating until the mixture is light and fluffy—this should take about 2–4 minutes.

Add the eggs and yolks one at a time, mixing thoroughly after each addition. Scrape down the sides of the bowl to ensure everything is well combined. Add the vanilla extract and mix just until blended.

Reduce the mixer speed to low. Add half of the dry ingredients, then mix until just combined. Pour in the milk and sour cream, mixing gently to incorporate. Finish by adding the remaining dry ingredients. Avoid overmixing, as this can make the cake dense.

Divide the batter evenly among the prepared pans. Bake for 24–26 minutes, or until a toothpick inserted into the center comes out clean.

Let the cakes cool in their pans for about 20 minutes, then transfer them to a wire rack. Once completely cool, wrap each layer in plastic wrap and refrigerate for at least 2 hours before frosting.