1 1/2 c. Ricotta
3/4 c. Parmesan cheese
2 tsp. grated onion
3 egg yolks
1 1/2 tsp. salt

In a large mixing bowl, combine the 1 1/2 cups of Ricotta, the 3/4 cup of grated Parmesan cheese, grated onion, 3 egg yolks and 1 1/2 teaspoons of salt and carefully stir them together until they are well mixed. Set aside until you have rolled out the dough.

Divide the pasta dough into four pieces and roll out the first one quarter of the dough to make it as thin as possible. Cover the rolled pasta with a damp towel to prevent its drying out, and roll out the second quarter of dough to a similar size and shape.

Using the sheet of rolled-out pasta as a sort of checkerboard, place a mound of about 1 tablespoon of the cheese-and-egg yolk mixture every 2 inches across and down the pasta. Dip a pastry brush into a bowl of water and make vertical and horizontal lines in a checkerboard pattern on the sheet of pasta, between the mounds of cheese filling. (The water will act as a bond to hold the finished ravioli together.) Carefully spread the second sheet of rolled out pasta on top of the first one, pressing down firmly around the filling and along the wetted lines.

With a sharp line cut the pasta into squares along the wetted lines. Separate the mounds of ravioli and set them aside on wax paper. In the same fashion, roll out and fill and cut the two other portions of dough.

To cook, drop the ravioli into 6 to 8 quarts of rapidly boiling salted water and stir them gently with a wooden spoon, to keep them from sticking to one another or the bottom of the pot. Boil the ravioli for 8 minutes or until they are tender, then drain in a large colander. Serve with tomato sauce.