Grate the peeled onions and potatoes and add the eggs to the mixture. Add the crumbled feta, milk, oil and salt to taste.
Smear a suitable oven dish generously with oil. Put 3 phyllo pastry sheets in it. Evenly distribute some of the prepared stuffing.
Place another 2 phyllo pastry sheets on top. Bake this patatnik in a moderate oven.
Before you take it out of the oven, sprinkle with grated cheese. Bake until golden.