Prepare the dough:
Place the flour on a board or in a bowl. Make a well in the center and crack the eggs into it. Beat the eggs with a fork until smooth. Using the tips of your fingers, mix the eggs with the flour, incorporating a little at a time, until everything is combined. Knead the pieces of dough together - with a bit of work they’ll all bind together to give you one big, smooth lump of dough! Once you’ve made your dough you need to knead and work it with your hands to develop the gluten in the flour, otherwise your pasta will be flabby and soft when you cook it, instead of springy and al dente. You just have to bash the dough about a bit with your hands, squashing it into the table, reshaping it, pulling it, stretching it, squashing it again. Then all you need to do is wrap it in cling film and put it in the fridge to rest for at least half an hour before you use it.
Make the tagliatelle:
Start rolling the dough from the top outer perimeter and when you have rolled one side, turn the dough 90° clockwise (a quarter turn) and roll the top side again and continue in this fashion. Remember to rotate the flat pasta circle while rolling to guarantee that all the sides are the same thickness.
Flatten it into a rectangle shape. Starting with one of the shorter sides of the rectangle, feed it through the rollers. Continue by turning the dial to the next narrowest setting (most likely number 2). Roll the pasta through the machine. At this point, it’s best to work with a helper, so one person can turn the crank and the other person can guide the dough into the machine with one hand and catch it with the other hand, being careful not to stretch or tear the sheet. Without folding the dough between settings, keep reducing the settings until the dough is rolled as thinly as you’d like. Once you’ve rolled your pasta the way you want it, you need to shape or cut it straight away.
Cook the pasta and make the dressing:
Cut the shallots and brown in a pan with the butter. Clean the mushrooms (porcini or other mixed mushrooms) and cut them into small pieces, then add them to the shallots, stirring to flavor. Continue cooking the mushrooms over low heat for about 10 minutes, adding white wine from time to time, then season with salt and pepper. Chop the walnuts coarsely and cook them in a pan with the oil for a couple of minutes then add the chopped walnuts to the mushrooms. Stir and cook the sauce for a couple of minutes. Meanwhile, cook the tagliatelle in abundant salted water, drain when al dente and pour them into the pan with the mushroom and walnut sauce. Add the Parmesan and sauté the tagliatelle for a couple of minutes more Serve the tagliatelle with porcini mushrooms and walnuts sprinkling with more Parmesan and pepper.