Step 1: After blanching, squeeze out as much liquid as possible from 8 ounces of nettles or kale.
Step 2: Mix with 2 cups ricotta, 3 yolks, 1 cup Parmesan and 1/2 teaspoon nutmeg in a bowl until well-combined.
Step 3: Season with salt and pepper to taste.
Step 4: Scoop the ricotta mixture into balls with a small ice cream scoop or a tablespoon.
Step 5: Pour the semolina into a shallow baking dish.
Step 6: Place the ricotta balls in the flour.
Step 7: Shake until the gnudi are thoroughly coated with flour.
Step 8: Place in the refrigerator, uncovered, for several hours or, preferably, overnight.
Step 9: Heat oven to 400 F.
Step 10: Heat large pot of salted water to a boil.
Step 11: Have ready a shallow baking dish with a thin layer of tomato sauce.
Step 12: Gently place gnudi in the boiling water. When the gnudi float, remove with a slotted spoon and place in the baking dish.
Step 13: Spoon a little of the remaining sauce on top of the gnudi.
Step 14: Sprinkle with Parmesan.
Step 15: Bake until bubbling and golden brown, 15 minutes.