Preheat your oven to 350°F (175°C) and prepare two 9-inch round pans by greasing and flouring them.
Cream together the softened unsalted butter and granulated sugar until light and fluffy, about 3-5 minutes.
Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract and lemon zest.
Whisk together the flour and baking powder in a separate bowl, then gradually add to the wet ingredients alternating with milk.
Pour the batter into prepared pans and bake for 25-30 minutes or until a toothpick comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.
Whip the heavy cream until soft peaks form, then gradually add powdered sugar and lemon extract until stiff peaks form.