Set your oven to 350°F (175°C). Grease and line three round cake pans with parchment paper—two for the vanilla layers and one for the chocolate layer. Set aside.

In a large mixing bowl, whisk together Greek yogurt, vegetable oil, softened butter, oat milk, and vanilla extract until smooth. Add the eggs one at a time, mixing well after each.

In another bowl, stir together flour, cornstarch, sugar, baking powder, and salt. Gradually add this dry mix to your wet ingredients, stirring just until combined. Try not to overmix.

Divide the vanilla batter evenly between the two prepared pans. Tap each pan gently on the counter to release any air bubbles. Bake for 30–35 minutes, or until a toothpick comes out clean. Let cakes cool in their pans for about 10 minutes, then turn them out onto a wire rack to cool completely.

In a clean bowl, whisk together flour, cocoa powder, baking powder, baking soda, espresso powder, cornstarch, salt, and sugar. Add the eggs, vanilla, and vegetable oil, and stir until smooth and well combined.

Pour the chocolate batter into the third prepared pan. Bake for 30–35 minutes. Let it cool in the pan for 10 minutes, then transfer it to a wire rack to finish cooling.

In a medium bowl, beat softened butter until light and fluffy. Add milk, vanilla, and a pinch of salt. Gradually mix in sifted powdered sugar until you have a light, creamy filling. Add a splash more milk if needed for spreading consistency.

Beat butter until creamy and smooth. Slowly add powdered sugar, then mix in cocoa powder, vanilla, and a pinch of salt. Add milk or cream a tablespoon at a time until your frosting is soft and spreadable.

If your cake layers have domed tops, use a serrated knife or cake leveler to trim them flat. This helps the layers stack evenly.

Place one vanilla layer on your serving plate or cake stand. Spread a layer of filling over the top. Add the chocolate layer, spread more filling, then finish with the second vanilla layer on top.

Start with a thin crumb coat (a light layer of frosting) all around the cake. Chill for 15 minutes to set. Then apply the final, thicker layer of frosting using an offset spatula. Smooth it out or go for a rustic finish—your call!

Finish it off with your favorite touches—sprinkles, chocolate curls, or piped frosting. Chill the cake for at least 30 minutes before slicing for clean cuts. Serve and enjoy every bite!