Blanch the spinach briefly in fiercely boiling water, drain, and refresh in ice–cold water. Squeeze in a kitchen towel until as dry as possible.
In a food processor, purée together the spinach, ricotta, egg yolks, 3 oz Parmesan, and seasoning. Spread out in a shallow tray, cover with plastic wrap, and allow to firm up in the fridge for a minimum of 3 hours.
Using two teaspoons, form the mixture into little balls and roll immediately in the flour.
In a large pan, bring at least 3½ pints lightly salted water to the boil, and at a gentle simmer poach the dumplings, five or six at a time, and remove with a slotted spoon after about 5 minutes when slightly swollen.
Transfer to a hot serving dish, cover, and keep warm.
Melt the butter until nut brown, throw in the sage leaves, turn until evenly coated and slightly crisp, and spoon over the dumplings together with the butter.
Sprinkle with the remaining Parmesan and serve with lemon wedges.