Mix hazelnuts with sugar. Coat a 9x13 inch baking pan with butter. Preheat oven to 350 degrees. Brush each sheet of filo dough with melted butter and stack in pan until 1/3 of the filo is used. Spread the nuts over the filo and continue layering and buttering. Pour any remaining butter over the top of the baklava and then press it down firmly with your hands. With a sharp knife, cut the baklava into diamond shaped pieces. Bake the baklava for 20 minutes. Reduce oven to 300 and place a piece of parchement paper over to retain pale color. Bake 30 minutes. Dissolve the sugar in the water, bring to a boil and simmer gently for 5 minutes. Stir in lemon juice and simmer for 4 minutes longer. Let cool. As soon as baklava is done, drain off any excess butter and pour syrup over baklava. Recut pieces and allow to stand for serveral hours before serving.