To make the filling: Trim the Swiss chard's stalks and reserve for another use. Wash the leaves well, and without shaking off the water, tuck the leaves into a 4-quart saucepan. Add 1/3 cup water, cover and cook over medium heat until wilted, 3 to 5 minutes. Drain and allow to cool. Squeeze the leaves as dry as possible, finely chop and transfer to a medium-sized bowl.

Whip the ricotta and stir it into the chard. Blend in the 3/4 cup Parmigiano-Reggiano, salt and pepper and nutmeg. Taste for balance. Beat in the egg. Cover and refrigerate until ready to use.

Filling the pasta: Stretch and thin the pasta to the thinnest setting on a pasta rolling machine. Cut the pasta into long strips about 4 1/2 inches wide. Cut each strip in half lengthwise. Keep the strips of pasta covered with plastic wrap until you are ready to work with them. Create diamond shapes by cutting each of the strips on the diagonal, spacing the cuts every 2 1/4 inches, so that each diamond's sides measure about 2 1/4 inches. Keep the cut pieces covered while you work with 1 or 2. Put a narrow row (about 1 teaspoon) of filling in the center of each diamond.

Place the pasta with the long strip of filling perpendicular to you. Fold the 2 points of the diamond on the left and right of the row of filling over each other, covering the filling. Pinch together the 2 overlapping pieces of pasta, using your thumb and forefinger to make a row of pinched closures down the length of the pasta. As you pinch together the pasta, twist it slightly to create an undulating ridge. This pleating will create a rippling, scalloped appearance.

Twist and seal the ends, creating tails. Place them in a single layer, without touching, on the towel-lined baskets. Uncover more of the cut pasta and repeat the process. Once the first batch is done, stretch and thin the next portion of the dough, and continue.

Cooking and serving the tortelli: Having a serving bowl and soup dishes warming in a low oven. Have a large colander ready for draining the tortelli. Bring 6 quarts water to a strong boil and add 2 tablespoons salt. Drop in the pastas and cook until their tails are pleasingly firm to the bite yet tender enough to eat. If freshly made, they will take about 3 to 4 minutes. If they have been done up to 24 hours ahead, they may need 8 to 10 minutes. While the pasta cooks, melt the butter in a small saucepan.

Gently pour the cooked tortelli into the colander, taking care not to break them. Carefully pour about 1/3 of the pastas into the heated serving bowl. Spoon a third of the butter over them, and then a generous sprinkling of the cheese. Top another with the third, and more butter and cheese. Finally pour in the last portion, top it with the remaining butter and cheese, and serve immediately. Pass any leftover cheese separately.