Slice the onion and soak it in cold water to remove the sharpness.

Lightly toast the tortilla on both sides in a dry pan.

Heat a pan and melt the butter slightly.

Crack an egg into the pan and cook.

Before the egg is fully cooked, place the sliced onion on top.

Add a slice of cheese on top of the onion.

Cover the egg mixture with the toasted tortilla.

Flip the tortilla carefully and sprinkle sugar on top of the egg.