Start with the preparation of the filling. Heat the olive oil in a large pan and sauté the chopped onion until soft. Take off the heat and add the spinach leaves, olives and capers. Mix together lightly until the spinach has wilted. Finally, mix in the herbs, tomatoes and potatoes. Adjust seasoning with salt and pepper. You can now start to fill the pies. Brush a sheet of filo pastry with butter. Cut into squares large enough to fit into your moulds. Criss-cross 4 layers of pastry into each mould. Fill with the spinach filling and top up with a piece of anchovy. Cover again with other 4 layers of pastry and press together the edges. Brush with a little more butter, prick with a fork and sprinkle with the sesame seeds. Bake in a hot oven at 170`c, for about 25 minutes, or until golden and pastry is crispy.