Step 1Heat oil in a Dutch oven or stock pot over medium. Add rosemary sprig and let fry in hot oil for 1 minute. Add onions and cook until they soften and start to caramelize, about 8 minutes. Remove and discard rosemary sprig.Add tomatoes and cook until tomatoes start to break down and release their juices, about 8 minutes. Stir in tomato paste, garlic, fennel seeds, and chili flakes; cook 3 to 4 minutes, until aromatic. Season generously with salt (I use about 3/4 teaspoon).
Step 2Add beans (with brine) and broth; bring mixture to a simmer. Simmer, uncovered, for 15 minutes, until the stew slightly reduces. Stir in Parmesan cheese and a few grinds of black pepper. Remove from heat and stir in vinegar. Taste and adjust seasonings as needed (you may want another pinch of salt).Ladle soup into bowls and garnish with fresh parsley, freshly grated Parmesan, and extra cracked black pepper. Serve with crusty bread.
