Recipe by epicurious.com 
5 cups all purpose flour, divided
1-1/2 teaspoons salt, divided
6 large eggs, divided
6 large egg yolks, divided
6 tablespoons (or more) water, divided
Place 2-1/2 cups flour and 3/4 teaspoon salt in processor; blend 5 seconds. Whisk 3 eggs, 3 yolks, and 3 tablespoons water in bowl.
With machine running, pour egg mixture through feed tube. Blend until sticky dough forms, adding water by teaspoonfuls if dry.
Scrape dough out onto floured work surface. Knead dough until smooth and no longer sticky, sprinkling lightly with flour as needed if sticky, about 8 minutes. Shape into ball. Cover with plastic wrap and let rest 45 minutes. Repeat with remaining flour, salt, eggs, yolks, and water.
Divide each dough ball into 4 pieces. Cover dough with plastic wrap.
Set pasta machine to widest setting. Flatten 1 dough piece into 3-inch-wide rectangle. Run through machine 5 times, dusting lightly with flour if sticking. Continue to run piece through machine, adjusting to next-narrower setting after every 5 passes, until dough is about 26 inches long. Cut crosswise into 3 equal pieces. Run each piece through machine, adjusting to next-narrower setting, until strip is scant 1/16 inch thick and 14 to 16 inches long. Return machine to original setting for each piece. Arrange strips in single layer on sheets of parchment.
Repeat with remaining dough. Let strips stand until slightly dry to touch, 20 to 30 minutes. Fold strips in half so short ends meet, then fold in half again. Cut strips into 2/3-inch-wide pappardelle. DO AHEAD: Can be made 1 day ahead. Arrange pappardelle in single layer on sheets of parchment. Stack sheets in roasting pan. Cover; chill.
Cook 4 -5 minutes in boiling salted water.