First, I preheat my oven to 350°F (175°C). I also prepare my 8-inch round cake pans by greasing and lining them with parchment paper. This ensures easy removal later.

In a large mixing bowl, I beat the softened butter and granulated sugar together until the mixture becomes light and fluffy. Then, I add the eggs one at a time, making sure to mix well after each addition. Next, I stir in the sourdough starter and vanilla extract until everything is combined.

In another bowl, I whisk together the all-purpose flour, baking powder, baking soda, and salt. This step is crucial to evenly distribute the leavening agents.

I gradually add the dry ingredients to the wet mixture, alternating with the buttermilk. I mix just until combined, being careful not to overmix, which helps keep the cake light and fluffy.

I divide the batter evenly between the prepared cake pans and smooth the tops with a spatula. I bake them in the preheated oven for about 25-30 minutes, or until a toothpick inserted in the center comes out clean.

Once baked, I let the cakes cool in their pans for about 10 minutes. Then, I carefully turn them out onto a cooling rack to cool completely.

While the cakes are cooling, I make the vanilla frosting. In a large bowl, I beat the softened butter until creamy. Gradually, I add powdered sugar, mixing until it’s well combined. Then, I stir in the vanilla extract and enough milk to reach my desired frosting consistency.

Once the cakes are completely cool, I place one layer on a serving plate. I spread a generous amount of vanilla frosting on top, then place the second layer on top and frost the top and sides of the cake. I like to make it look pretty by adding decorative swirls!