Preparation

Make the dumplings:

• Simmer the whole potatoes in ­lightly salted water until tender enough to allow a knife point to easily penetrate to the center. Drain and cool slightly.
• Blanch the sorrel in boiling water for a few seconds and refresh in cold water. Drain thoroughly and press out excess moisture. In a food processor or blender, purée the sorrel with the olive oil and egg yolks.
• Cut the potatoes into smaller pieces and pass them through a food mill or a ricer (the skins will stay behind) into a mixing bowl. Add the semolina, flour, breadcrumbs, puréed sorrel, nutmeg, salt, and pepper to taste. Knead the mixture lightly until it comes together to make an even dough. Cover the bowl with a towel and let rest for 30 minutes.
• Lightly flour your hands and the work surface. Divide the dough into a few pieces and roll each piece into a 3/4-in. rope. Cut the ropes into 2-in. pieces. Roll the ends of each piece to taper them and make football-shaped dump­lings.
• Cook the dumplings in a large pot of boiling salted water until they float to the top and feel firm, about 4 minutes. Remove with a slotted spoon, drain, and toss with a ­little oil to prevent sticking. Use immediately or refrigerate.

Make the sauce:

• Combine the fish stock, shallots, and garlic in a small, nonreactive saucepan and simmer until reduced to about 2/3 cup. Put the sorrel leaves into the bowl of a food processor, add the hot stock reduction, and process about 30 seconds. With the ­motor running, gradually add the olive oil and salt and pepper to taste. Keep warm until ready to serve. The sauce may separate on standing, so whisk it well before serving.

To finish the dish:

• Run your finger over the salmon fillets to find any pin bones and pull them out with tweezers or by pinching them between your finger and a knife. Season with salt and pepper to taste. Set up a ­steamer (or a large pot fitted with a rack), bring the ­water to a boil, put in the fish, cover, and steam until just barely done in the center, 5 to 10 minutes, depending on the shape of the fillet.
• Meanwhile, sauté the dumplings in a ­little oil or butter in a nonstick pan over medium-high heat until they’re heated through and slightly browned.  Ladle some warm sauce on each plate, arrange a few dump­lings on one side and a salmon fillet on the other. Decorate with more greens, if you like, and serve immediately.