Cook and rice the potatoes following the dough recipe. While they are cooling, make the offelle filling.

Melt the butter in the skillet over medium heat and stir in the chopped onion. Season with ¼ teaspoon salt and cook until the onion wilts. Crumble in the sausage and ground veal. Salt again lightly and fry the meats for a couple of minutes, stirring and breaking up any lumps, until browned. Heap the spinach in the pan, raise the heat, sprinkle the remaining salt over and toss well. Drizzle a few tablespoons of water into the pan and stir steadily as the leaves soften and release their liquid. Cook over moderate heat, stirring frequently (and scraping up any caramelization in the skillet), until the spinach is fully cooked and all of its moisture has evaporated. Remove from the heat and let cool (to cool rapidly, spread the filling on a plate).

While the filling cools, mix the potato dough. To form the offelle, cut the dough in 4 pieces; work with one and keep the others covered. Dust the work surface and rolling pin liberally with flour and roll out the dough to a 12-inch round or slightly larger. Keep the dough from sticking by sliding a spatula or dough scraper under it and flouring the surface frequently. Cut 4-inch circles in the dough, using a round pastry cutter or the rim of a container or jar, dipped in flour. Remove the scraps of dough between the circles and loosen them with the spatula.

Drop 2 teaspoons of filling on each circle and fold the dough over, into a half-moon, with the filling enclosed. One at a time, pick up the offelle and pinch the edges of dough together with floured fingers. Turn the edges inward, in small overlapping folds, and crimp to seal. Place completed offelle on a floured tray in a single layer, spaced apart. Press the scraps into another cut piece of dough and form offelle the same way.

Meanwhile, bring 8 quarts of water with 2 tablespoons salt to a rolling boil, as you want to cook offelle right away. (Otherwise, freeze them solid on the tray then pack in air-tight containers.) For dressing the offelle, put the butter in the big sauté pan or skillet, set it over low heat to melt, toss in the sage leaves and grind in a generous amount of black pepper. Keep the sauce warm—but not cooking—so the sage leaves infuse the melted butter.

When the water is at a rolling boil, quickly brush off excess flour and drop half the offelle and drop them into the pot. Stir, cover the pot, and return to the boil over high heat. As the offelle rise to the surface; turn and stir them occasionally so they cook evenly and don’t stick to each other. Boil for about 6 minutes until cooked through—check for doneness by biting into one on the edge where the dough is thickest.

Lift out the offelle with a spider, drain briefly and spill them into the warm butter in the pan. Tumble them in the pan and shake it so the butter flows all around them. Return the water to the rolling boil and cook the remaining offelle. Drain and drop them in the pan, on top of the first batch. Raise the heat slightly, turn and tumble the offelle and shake the pan, until all are hot and coated with sage butter.

Turn off the heat and sprinkle half of grated cheese on top. Spoon portions of offelle onto warm plates, drizzle any hot sage butter left in the pan over each portion, and serve right away. Pass more cheese at the table.