Whisk the egg, water and salt in a bowl.

Slowly add flour and knead.

Separate the dough into the lumps, cover it and let it rest for 30 minutes.

Grind the cheese with a fork.

Chop the onion and mix it with the cheese.

Add chopped parsley.

Spread the dough on a floured surface.

Cut squares with a width of 6 cm.

Place the cheese mixture on the ends and close it in a triangle shape.

Press the edges with the fork to make them stick.

Cook in boiling salted water until tender.

Melt the butter in a frying pan and fry with tomato paste.

Put the ravioli on the serving plate.

Pour the tomato sauce on top and serve hot.