In a large bowl, sift the flour, make a well in the center. Combine the sugar and the egg yolks in the well. Whisk slowly adding the cold melted butter and the grated lemon zest. Blend to a light consistency. Pour the mixture into a buttered and floured cake pan. Bake in a hot oven (350 F). When the cake is golden, cover with parchment paper. Check the cake with the blade of a knife. It should come out clean. Unmold on a rack and leave to cool.
