Put the flour, cocoa, sugar and pinch of salt on a clean wood or marble work surface and use a fork to blend it. Form the dough into a circle and make a well in the middle; break the eggs into the well.
Using a fork, gradually draw the flour mixture into the well, mixing and scrape in a circular motion. Continue until all of the flour is incorporated, sprinkling the mixture with a little of the water as needed. The dough should be fairly stiff but not crumbly. Gather the dough into a ball.
Sprinkle your work surface generously with flour and knead the dough for 10 minutes. To knead, set the dough in the center of the work surface. Push the heel of your right hand into the dough and then press it away from you. Turn the dough a quarter turn and repeat. Continue until the dough is very smooth and satiny.
Cover the dough and let rest 30 minutes.
While the dough rests, make the sauce and set it aside.
To finish the pasta, set up a pasta machine and put the rollers on the widest setting.
Cut the dough into four pieces.
Sprinkle a baking sheet with flour.
Crank each piece of dough through the machine, fold it in half crosswise and crank it through again. Repeat twice. Change the rollers to the next setting and roll the dough through 3 or 4 times. Continue through three more settings. When you finish a piece, set it on the floured baking sheet.
At this point, the dough may be so long that you should cut it in half crosswise. Crank each piece through the narrowest setting.
Crank the rolled pasta through the fettuccine cutter, set the cut fettuccine on the baking sheet and sprinkle with a little flour.
Cook the pasta immediately or wrap it tightly in plastic wrap and chill for up to two days.
To cook, fill a large pot two-thirds full with water, add 1 tablespoon kosher salt and bring to a boil over high heat. When the water has reached a rolling boil, add the pasta, stir and cook for 60 to 90 seconds, until the pasta is tender but not mushy.
Drain the pasta thoroughly and transfer to warm soup plates. Top with sauce and use two forks to gently lift the pasta and allow the sauce to coat it. Spoon the berries on top, garnish with mint leaves and serve immediately.
Variations: If you don't want to bother with the vanilla sauce, you can serve the chocolate pasta with strawberry sauce. Use 3 cups a sliced strawberries mixed with a third of a cup of sugar. Chill them for at least two hours and then pass them through a food mill. Taste and add more sugar if they taste a little flat. Add 2 or 3 tablespoons of orange liqueur, raspberry liqueur or Kirsch, toss and spoon over the pasta. Serve immediately.
Before you begin the sauce, have everything else - the chocolate pasta, cooking water, warm serving bowls - ready. The sauce must be served within minutes of taking it off the stove.
For Vanilla Sauce: Fill the bottom of a double boiler or a medium saucepan with water and bring to a boil over high heat. Reduce the heat to medium.
Put the egg yolks in the top part of a double boiler or in a copper or stainless steel bowl that will sit on top of the saucepan. Whisk the eggs vigorously until they turn pale yellow. Whisk in the sugar and salt. Set the eggs over the boiling water and whisk constantly as they increase in volume. Turn the bowl frequently to avoid hot spots.
Whisk in the sherry, lemon juice and vanilla extract and continue to beat the mixture until it has doubled in volume and is smooth and glossy. Be sure to beat too long. If the sauce begins to deflate stop immediately and remove from the heat.