Peel the onions, cut them in half and then in thin slices. Boil the sliced onions in salted water for 20 minutes. When boiled, drain and allow cooling in a colander. Once cool, squeeze them in your hands to strain them completely. Place the strained onion slices in a bowl. Grate the cheeses. Add the grated cheeses, dill, 3 eggs and flour. Add salt and pepper and mix well. Follow the instructions to make the pie, which you'll bake in a preheated oven, on the lowest shelf of the oven, at 190°C for 50 minutes. For the final 10 minutes of baking, place the baking tin on the bottom of the oven to bake the pies base more thoroughly.

For making Pie in a Rectangular Baking Tin:
Brush the bottom and sides of a rectangular tin liberally with olive oil. Lay a shortcrust pastry sheet in the pan and use a fork to make small holes all over its surface. Empty the filling over the pastry and cover with the remaining pastry sheet. Fold the overhanging pastry neatly under the rim of the pan, and press the edges together using your fingers. Beat 1 egg and brush the surface of the top sheet. Cut the surface into portions in order for steam to be released during cooking.