Stir the breadcrumbs, flour and fine salt together in a mixing bowl. Pour in 180 ml of hot water, stir with a wooden spoon until shaggy, then tip onto the counter and knead for 2 minutes. Add up to 20 ml more water if the dough crumbles, or a tablespoon of flour if it sticks to your palm, until it feels like soft modeling clay.

Cut the dough into 4 pieces and roll each into a rope about 1 cm thick, keeping the rest under a damp towel. Cut each rope into 1 cm pieces, press each with your thumb and drag it slightly toward you to make a shallow curl. Set the pisarei in a single layer on a floured 33 x 46 cm / 13 x 18 inch sheet pan. You'll have a few hundred, and shaping takes about 20 minutes.

Warm the olive oil and pancetta in a 28 cm / 11-inch deep sauté pan over medium heat for 3 minutes, until the fat renders and the edges turn pale gold. Add the onion, carrot, celery and a pinch of salt, and cook over medium-low heat for 7 minutes, until soft and translucent but not browned.

Stir in the tomato paste for 1 minute, then add the passata, borlotti beans and broth. Simmer gently, uncovered, for 15 minutes, mashing a ladleful of beans against the side of the pan halfway through so the sauce thickens and coats a spoon. While it simmers, bring 4 litres of water to a boil in a 24 cm / 5-quart (4.7 L) pot and add the coarse salt.

Boil the pisarei in the salted water for 4 to 5 minutes. They rise to the surface after about 2 minutes, but keep cooking and bite one: the center should be tender with no dry floury spot. Scoop out 120 ml of the cooking water, then lift the dumplings into the sauce with a slotted spoon.

Toss over low heat for 1 minute, adding cooking water a splash at a time until the sauce loosens and coats the dumplings. Off the heat, stir in half the Grana Padano, taste for salt, and serve with black pepper and the remaining cheese.