Preheat the oven to 200C (400F). You will need a large deep baking dish/oven tray, about 40 cm x 30 cm (16 x 12″).
Put the oil into the baking dish and place in the oven to heat.
Squeeze the grated potatoes with your hands until dry.
Place in a bowl with the eggs, onions and matzo meal and mix together. Season to taste with salt and pepper.
Carefully remove the hot baking dish from the oven and spoon the mixture into the oil, spreading it out to cover the base without pressing down to firmly.
Bake for 1 hour 15 minutes until golden.
You can eat immediately, but it is easier to cut if you allow it to cool, and then cut into large squares. Reheat in a very hot oven until piping hot, brown and sizzling.