In the electric mixer, mix the butter until it is creamy. Add the wheat flour little by little and stirring constantly, add the sugar and lemon zest. Pour the mixture into a greased 9 x 13 x2 pan and covered with greaseproof parchment or aluminum foil.

Bake at 325 degrees for 15 minutes.

Prepare the deck. Beat the whites until stiff and add the yolks one by one and continue beating. Add sugar little by little and beating constantly until creamy. Add the lemon juice, flour and lemon zest. Pour the mixture over the crust.

Bake 325 degrees for 30 minutes. Let cool, cut into squares and decorate with confection sugar.