How to Make It
Preheat the oven to 375°. Bake the potatoes for about 45 minutes, or until soft. Let cool slightly, then peel and pass them through a ricer or coarse sieve into a bowl. Stir in the cream, egg yolks, Parmesan, nutmeg, thyme, salt and pepper. Stir in the flour to make a soft, slightly sticky dough. Shape into a ball, wrap in plastic and refrigerate for at least 1 hour or overnight.
Divide the dough into 3 pieces. On a lightly floured surface, roll each piece of the dough into a 16-inch-long rope, about 1/2 inch wide. Cut crosswise into 3/4 -inch pieces. Lightly dust with flour and roll each piece down the back of a fork with your thumb to make long grooves on the gnocchi. Spread the gnocchi on a floured baking sheet. Refrigerate until chilled, about 2 hours.
Cook the gnocchi in 2 batches in a saucepan of boiling salted water until they float to the surface, about 2 minutes. Transfer them to a bowl of ice water, then to paper towels.
In a bowl, season the sherry vinegar with salt and pepper. Whisk in the truffle and olive oils.
Preheat the oven to 500°. In a nonreactive skillet, cook the pancetta over moderately high heat, stirring, until crisp and browned. Transfer to a plate and discard the fat. Add the butter to the skillet, and when it is golden, add the gnocchi. Cook until they brown around the edges, about 3 minutes. Put the skillet in the oven and roast for about 5 minutes, stirring often, until browned all over. Add to the pancetta.
Add the shallot to the skillet and sauté until lightly browned. Add the garlic and thyme and cook for 1 minute. Stir in the gnocchi, pancetta and the sherry vinaigrette and season with salt and pepper.
In a large bowl, toss the frisée with the gnocchi mixture and then with the dressing. Mound the salad on 8 plates. Garnish with the Parmesan shavings and chives and serve.