Put the potatoes on to boil. When they are cooked, peel and mash them without adding any more liquid.
Meanwhile, wash the spinach and cook it without adding any extra water. Drain, squeezing out as much liquid as possible, and chop finely.
Mix the ptotaotes and spinach with all the other ingredients except for 1 tablespoons of the Parmasan cheese and half the butter. Be generous with the pepper. Chill for 45 minutes.
Preheat the oven to 400 degrees F and bring a large kettle of salted water to the boil.
To cook the gnocchi, drop teaspoonful of the mixture into the kettle, a few at a time. Keep the water boiling. The gnocchi are done when they rise to the surface, after only a couple of minutes.
Remove them with a slotted spoon to an ovenproof dish and repeat the process until all the gnocchi are cooked.
Melt the remaining butter and pour it over the gnocchi.
SDprinkle the rest of the Parmasan over the top and bake for about 10 minutes, or until well browned.
Serve very hot.