Roast potatoes 45 minutes at 425°F or boil them in their jackets/skins until very tender, 25-30 minutes. Cool potatoes completely. Remove potatoes from their skins and pass through a ricer. Arrange riced potatoes on a large work surface with a well at center. Place yolks in well along with the cheese. Season with salt, pepper and a little nutmeg. Work eggs and cheese into potatoes first then sprinkle 2 cups flour over the potatoes and work it into the potatoes. Work spinach into potatoes, if using. If dough is sticky, sprinkle in a little more flour until firm enough to roll into ropes on a floured surface. Cut into 1-inch pieces or pillows for basic dumplings or, use a gnocchi tool to roll and mark the dumplings. Transfer gnocchi to a parchment-lined baking sheet.
Boil gnocchi in salted water in 2 batches until they float and are cooked through. Remove with a spider to a warm bowl, carefully drain excess water from the bowl and serve with pomodoro sauce or pesto.