Wash the chard and wilt the leaves in a 26 cm / 10-inch skillet with a splash of water over medium heat for 4 to 5 minutes, until fully collapsed.

Drain, cool, then squeeze the chard very dry by hand, twice if needed. Chop it finely.

In a large bowl, combine the chopped chard, ricotta, 100 g Parmigiano, egg yolk, nutmeg, salt, and pepper. Mix until uniform and chill while you make the dough.

Mound the flour on a work surface with a well in the center. Crack in the eggs with a pinch of salt and whisk, gradually pulling in flour from the edges.

Knead the dough for 8 to 10 minutes until smooth and elastic. Wrap in plastic and rest at room temperature for 30 minutes.

Divide the dough into 4 pieces. Roll each through a pasta machine or by hand to about 1 to 2 mm thick, keeping the rest covered.

Lay a sheet on a floured surface and spoon teaspoon-sized mounds of filling, about 12 to 15 g each, in a row 5 cm apart.

Fold the dough over the filling, press out any air, and seal the edges firmly. Cut into squares with a pastry wheel. Repeat with the remaining dough, makes about 36 to 40 tortelli.

Bring a 5-quart / 4.7 L pot of well-salted water to a boil. Melt the butter with sage in the 26 cm skillet over low heat for 3 to 4 minutes, until the butter smells nutty and the sage crisps slightly. Watch closely, it burns fast once it starts foaming.

Cook the tortelli in two batches so the pot doesn't crowd, 3 to 4 minutes each, until they float and the pasta at the seams is tender.

Lift the tortelli with a slotted spoon straight into the sage butter and toss gently, adding a splash of pasta water if needed.

Plate immediately, topping with the extra Parmigiano and black pepper.