Dice the potato and onion into 1cm cubes, and slice the sausage into rounds.

Boil the diced potato until partially cooked, then drain. Heat oil in a pan, sauté the sausage and onion, then add the potato and fry until golden.

Whisk 3 eggs and season with a pinch of salt and pepper.

Pour the egg mixture into the pan over the sautéed vegetables and sausage. Add cheddar cheese slice and mozzarella cheese on top once the egg starts to set.