Divide dough in half so that immediately form large rectangles. Melt the butter. Grease an ovenproof dish (20×30 cm) with a little butter. Pour 15 layers of filo dough on top of each other, spreading each layer thinly with butter.
Chop the pistachios and sprinkle them, except for 2 tbsp, on the dough. Place remaining pastry sheets on top, repeatedly brushing each with a tiny bit of butter. Cut into about 27 small rectangles with a sharp kitchen knife. Pour the remaining butter on top. Bake in a heated oven (E- Kitchen oven: 200 °C /Umluft: 175 °C Gas: level 3) for 45-55 min. until golden brown – the top layers of dough should already be rising.
Cover after 20-25 min. Heat sugar, juice of one lemon and 400 ml water in a saucepan at low temperature and stir until sugar is completely dissolved. Bring to a boil and cook at low temperature for about 20 min to make syrup. Remove the baklava from the heat and pour the hot syrup over it. Cool. Before serving, finely grind remaining pistachios and sprinkle on top.