Preheat the oven to 350 degrees.In a kitchen stand up mixer blend sugar, vanilla sugar and butter together until light and fluffy. Add the egg and mix well again.Add the lemon zest, flour, walnuts and baking powder and mix until everything is well incorporated.Spray the cookie molds with nonstick spray and fill them by pressing the cookie dough in about 2/3 of the way up. Bake them for about 15 minutes until they are light golden brown. Leave them in the molds for about 5 minutes to cool slightly, then invert them and clean the molds, re-spray them and repeat the process until you run out of the dough.Once they are cool dust them liberally with confectioners sugar. They taste better the next day!