Preheat oven to 350 F
Butter a 9 inch round baking pan.
Melt butter and set aside. Grate zest of the lemon.
Pour eggs and sugar into a bowl of an electric mixer fitted with the paddle attachment. Mix until pale and fluffy. Add vanilla, lemon zest and lemon juice. Then pour in melted butter. Mix carefully.
Sift in flour and with a wooden spoon mix flour into the batter with big movements. Its important that air remains in the batter.
Pour batter in the baking pan and bake for 25-30 min until done.
Let cool in the pan on a wire rack.
Sprinke with icing sugar
Whipped cream and fresh raspberries (optional).