3 tablespoons extra-virgin olive oil
1 large red onion, chopped
2 large stalks celery, chopped
4 cloves garlic, chopped
2 large carrots, diced
1/4 pound thinly sliced pancetta, cut into thin strips
1/2 head Savoy cabbage, finely sliced, blanched and drained
1/2 bunch Swiss chard, finely sliced
1 large waxy potato, cut into 1/2-inch cubes
4 cups low-sodium chicken stock
3 medium tomatoes, seeded and diced
1 bouquet garni (1 sprig rosemary, 4 sprigs thyme, 1 bay leaf and 1 bunch parsley, tied together with kitchen twine)
3 cups cannellini beans (canned or cooked dried beans)
1 cup spinach, coarsely chopped
Kosher salt and freshly ground pepper
Grated Parmigiano-Reggiano cheese, for topping