Step 1

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.

Step 2

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.