2 15-oz. cans cannellini beans, rinsed and drained
1 small head escarole, chopped into 1- to 2-inch pieces, washed, and lightly dried
1 cup low-salt canned chicken broth
1-1/2 tsp. red-wine vinegar; more to taste
1/4 cup freshly grated Parmigiano-Reggiano
Heat the oil in a heavy 5- to 6-qt. Dutch oven over medium heat. Add the onion and cook, stirring occasionally, until tender, 5 to 6 minutes. Add the sausage, raise the heat to medium high, and cook, stirring and breaking up the sausage with a wooden spoon or spatula until lightly browned and broken into small (1-inch) pieces, 5 to 6 minutes. Add the garlic and cook for 1 minute, then stir in the beans. Add the escarole to the pot in batches; using tongs, toss with the sausage mixture to wilt the escarole and make room for more.
When all the escarole is in, add the chicken broth, cover the pot, and cook until the beans are heated through and the escarole is tender, about 8 minutes. Season to taste with the vinegar and salt. Transfer to bowls and sprinkle each portion with some of the Parmigiano.