Preparation:

Boil the potatoes for an hour, then peel them and mash them. Roll out the potato mash on a smooth surface and let it cool. Sauté the onion in olive oil until golden-brown. If the onion starts burning, add some warm water or stock. Stir in the chopped sausage, herbs and spinach. Season to taste. When ready, mince everything in a grinder.
Use the potatoes to make a dough as if you were preparing gnocchi. You will knead the potatoes with flour, one egg and 30 g butter. Use a rolling pin to make discs (1 cm hight and 6 cm in diameter). Put the filling in the middle of the disc and fold it in a half-moon shape. Cook the fagottini in boiling water and when they start floating to the top, take them out of the water and sauté with butter and cheese in a frying pan. Use high quality butter to get a rich and creamy texture.