Roll out the pasta dough to the thinnest setting on a pasta machine. Cut the dough crosswise into 1/4-inch strips. Place the tagliatelle on a sheet tray that has been dusted with semolina flour, cover with a clean dish towel, and set aside until ready to use.
Bring 6 quarts of water to a boil and add 2 tablespoons of salt.
In a 12 to 14-inch saute pan, cook the pancetta over high heat until it is browned and the fat has been rendered, about 10 minutes. Add the butter and parsnips and saute over high heat without shaking the pan too much until they are golden brown and slightly crispy, 5 to 6 minutes. Season, to taste, with salt and pepper, add the parsley, and cook 1 minute longer.
Cook the tagliatelle in the boiling water until tender yet al dente, about 2 minutes. Drain the pasta, reserving some of the cooking water, and add the pasta to the pan with the pancetta and the parsnips. Toss over high heat to coat the pasta, adding pasta cooking water if necessary to keep the sauce form getting too tight. Divide equally among 4 heated pasta bowls, grate Parmigiano-Reggiano over the top of each bowl, and serve immediately.
Mound 3 cups of flour in the center of a large wooden cutting board. Make a well in the middle of the flour, add the eggs. Using a fork, beat together the eggs and begin to incorporate the flour starting with the inner rim of the well. As you incorporate the eggs, keep pushing the flour up to retain the well shape (do not worry if it looks messy). The dough will come together in a shaggy mass when about half of the flour is incorporated.
Start kneading the dough with both hands, primarily using the palms of your hands. Add more flour, in 1/2-cup increments, if the dough is too sticky. Once the dough is a cohesive mass, remove the dough from the board and scrape up any left over dry bits. Lightly flour the board and continue kneading for 3 more minutes. The dough should be elastic and a little sticky. Continue to knead for another 3 minutes, remembering to dust your board with flour when necessary. Wrap the dough in plastic wrap and set aside for 20 minutes at room temperature. Roll and form as desired.
Note: Do not skip the kneading or resting portion of this recipe, they are essential for a light pasta.
Yield: 1 pound of pasta, about 4 servings