03Bring a large pot of water to a boil and salt it. Divide the dough in half. Turn one half of the dough onto a lightly floured surface and roll it into a large rectangle no thicker than 1/4 inch and ideally closer to 1/8 inch, adding additional flour sparingly as necessary. Repeat with the rest of the dough.04Cut into squares no larger than 4 inches across. Drop the squares into the water and cook until tender, 2 to 3 minutes. Drain, reserving a little of the cooking water. Toss the handkerchiefs with the pesto, some salt and pepper, and a spoonful of cooking water, if necessary, to thin the pesto. Serve immediately, garnished with Parmesan.