GNOCCHI
1 1/2 pounds Yukon Gold potatoes, peeled and quartered
6 large egg yolks
1 1/3 cups all-purpose flour, plus more for dusting
1/2 teaspoon kosher salt Pinch of freshly grated nutmeg

CRAB SAUCE
1 quart fish stock
2 fresh blue crabs
1 tablespoon extra-virgin olive oil
1 small onion, finely chopped
1/4 small fennel bulb, finely chopped
2 garlic cloves, minced
1 teaspoon crushed red pepper
3/4 cup heavy cream
3/4 cup dry vermouth
1/2 teaspoon thyme leaves, chopped
1 tarragon sprig 1 bay leaf
3/4 pound jumbo lump crabmeat
3 tablespoons unsalted butter Kosher salt Shaved Parmigiano-Reggiano cheese, for garnish

Step 1 Make the gnocchi
In a saucepan, cover the potatoes with 1 inch of water and cook over moderate heat until tender, 15 minutes; drain and pass through a food mill or ricer into a bowl. Add the egg yolks, 1 1/3 cups of flour, salt and nutmeg; gently mix until the dough starts to come together. Gently knead on a floured work surface, dusting with flour if sticky. Divide the dough into 4 equal pieces.

Roll out one piece of dough into a 3/4-inch-thick rope; keep the remaining dough covered with a damp kitchen towel. Cut the rope into 1-inch pieces and lightly dust with flour. Roll each piece against the tines of a fork or a gnocchi paddle to make ridges. Transfer the gnocchi to a lightly floured baking sheet. Repeat with the remaining dough.

Working in 2 batches, cook the gnocchi in a large pot of salted boiling water until they rise to the surface, about 2 minutes. Then simmer until just cooked through, 1 to 2 minutes. Transfer to an ice bath and let cool. Drain well and let dry on paper towels.

Step 2 Make the crab sauce
In a saucepan, bring the stock to a simmer. Add the crabs, cover partially and simmer over high heat until the liquid is reduced to 2 cups, 15 minutes. Strain into a bowl; discard the crabs.

In the same saucepan, heat the olive oil. Add the onion, fennel, garlic and crushed red pepper and cook over moderate heat, stirring, until tender, 5 minutes. Add the reduced crab stock, cream, vermouth, thyme, tarragon and bay leaf and bring to a boil. Simmer over moderately high heat until reduced to 2 cups, 15 minutes. Discard the tarragon and bay leaf.

In a skillet, heat half of the pan sauce. Add half of the gnocchi and cook over moderate heat until hot, 2 minutes. Add half of the crab and 1 1/2 tablespoons of the butter; cook until warmed through and the sauce is slightly thickened, 2 minutes. Season with salt and transfer to a platter. Repeat with the remaining pan sauce, gnocchi, crab and butter. Garnish with the cheese and serve at once.