Preheat broiler.

Peel lemon, leaving all white pith behind; cut rind into slivers and set aside, reserving lemon.

Arrange sausage on a baking sheet and prick several times. Broil, turning once, until browned on both sides. Transfer sausage to a platter and set aside; drain any accumulated oil into a 12-inch skillet and add enough olive oil to make ¼ cup. Place over medium heat; when hot, add onion and cook, stirring occasionally, until soft; add garlic, rosemary, and slivered lemon peel and cook for 2 minutes. Add the cannellini beans and chicken stock to desired consistency; more for a soupy dish, less for more of a stew. Bring to a simmer, taste, and add salt and pepper as desired. Cut sausage into serving pieces and nestle into beans; cover and simmer for 10 minutes, stirring occasionally.

Cut reserved lemon into wedges and have on the table for diners to spritz as desired. Serve with French bread.