Preheat oven to 350°F (175°C). Grease and flour an 8-inch cake pan.
In a bowl, mix flour and baking powder.
In a separate bowl, cream together butter and granulated sugar until light and fluffy. Beat in eggs one at a time.
Mix in lemon zest and lemon juice.
Gradually add the flour mixture alternately with milk, starting and ending with flour.
Pour batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
Whip heavy cream with powdered sugar and vanilla extract until stiff peaks form.
Spread whipped cream over the top of the cooled cake.