Make the pasta dough. Cover and leave it to rest at room temperature for about 30 minutes.
To make the filling, cook the spinach in lightly salted, boiling water for about 5 minutes. Drain well and when it has cooled a little, squeeze out the excess water. Melt the butter in a frying pan and sauté the spinach to dry it out. When it has cooled a little, chop it finely on a wooden board.