For the pastry, place the flour and salt into the bowl of an electric mixer. Cut the margarine into cubes and start kneading with a hook until the mixture resembles breadcrumbs. Pour in the cold water and knead just to bind, taking care not to over knead as this will result in a tough dough. Cover dough with cling film and rest in a refrigerator for approximately 20 minutes. Meanwhile, prepare the filling. Cook the onion in 2 tbsp. olive oil till soft, add in garlic and anchovies and continue to cook for another minute. Stir in the remaining ingredients, remove off the heat and allow to cool down completely. Roll the dough onto a lightly dusted surface with flour into 5mm thick 15cm discs. Place spoonful of the spinach filling in the centre and brush the edges with a little of the beaten egg. Next, pinch the edges firmly to form the qassatat and retain a hole in the centre. Transfer onto a greased baking tray, brush with the remaining beaten egg and bake at 180°C for approximately 20 minutes or until cooked through and lightly golden.