How to Make It
Place the flour, cocoa powder, powdered sugar, and salt in the bowl of a food processor; pulse to combine. Add the eggs and vanilla extract. Process for 30 to 60 seconds or until the dough comes together in a shaggy ball.
Transfer the dough to a lightly floured work surface and knead for 1 to 2 minutes or until the surface of the dough is smooth. Shape dough into a disc; wrap with plastic wrap and let rest in the refrigerator for 30 minutes.
Remove dough from the refrigerator and cut into four equal pieces. Working with one piece at a time (keeping the others covered in plastic), flatten the dough and run through the widest setting of your pasta roller. Fold one of the one end of the dough lengthwise into the center. Then, fold the other end over the first folded end, forming a letter shape. Run the folded dough through the widest setting of your pasta roller, repeating the folding and rolling process two more times.
Run the pasta sheet through each successively smaller setting, twice for each setting, until it reaches your desired thinness (we stopped at setting 4 on our KitchenAid attachment).
Lightly flour both sides of the dough, cut in half and place on a floured baking sheet. Repeat this process with the 3 remaining portions of dough.
Run each piece of dough through the fettuccine attachment (or cut by hand into 1/2-inch ribbons) and lightly dust with flour to keep the pasta from sticking together.
Bring a large pot of lightly salted water to a boil. Add pasta to pan and cook for 2 to 3 minutes, or until desired tenderness. Drain. Divide pasta among serving bowls. Top as desired.