In a large bowl, beat the butter, oil, and sugar together until the mixture becomes pale, soft, and fluffy in texture.

Add the eggs one at a time, mixing thoroughly after each addition so everything blends smoothly. Once done, stir in the vanilla extract.

In a separate bowl, combine the flour, baking powder, and salt. Add this dry mix into the wet mixture little by little, alternating with buttermilk. Mix gently after each addition until the batter is smooth and well combined.

Pour the batter evenly into the prepared pans. Bake for 35–40 minutes, or until a toothpick inserted in the center comes out clean. Let the cakes cool completely before removing them from the pans.

To make the lemon curd, first rub the sugar and lemon zest together to release the aroma. Then add egg yolks and lemon juice into a saucepan and mix well.

Cook the mixture on low heat while stirring continuously. Keep stirring until it thickens into a smooth, creamy curd. Remove from heat, mix in cold butter, strain for a silky texture, and let it chill.

For the frosting, beat the butter until soft and creamy. Slowly add sugar while mixing, then pour in cream, vanilla, and a pinch of salt. Continue whipping until the frosting becomes light and fluffy.

To assemble, place one cake layer on a plate, spread lemon curd evenly on top, then add the second layer. Cover the entire cake with frosting, smooth it out, and chill before serving so it sets nicely.