Preheat oven to 350°F (175°C) and prepare two 9-inch round cake pans by greasing with butter and dusting with flour.

In a mixing bowl, cream together softened butter and sugar using an electric mixer until light and fluffy. Gradually add eggs one at a time, mixing well. Stir in vanilla extract and lemon zest.

In a separate bowl, whisk together flour and baking powder. Gradually add to the wet ingredients, alternating with milk. Mix until just combined.

Divide the batter evenly between the prepared pans and bake for 25-30 minutes, until a toothpick comes out clean. Cool in pans for 10 minutes before transferring to wire racks.

For the frosting, whip heavy cream until soft peaks form. Gradually add powdered sugar and lemon extract, continuing to whip until stiff peaks form.

Once cakes are cool, place one layer on a plate and spread a portion of frosting. Place the second layer on top and frost the entire cake. Chill for at least 1 hour before serving.