Pasta with Beans, Chard, and Rosemary

Heat oil in Dutch oven over medium-high heat until smoking. Add pancetta and cook, stirring occasionally, until pancetta begins to brown, 2 to 3 minutes. Stir in onion and chard stems and cook, stirring occasionally, until slightly softened, about 3 minutes. Add 1 teaspoon rosemary, garlic, and pepper flakes and cook until fragrant, about 1 minute. Stir in beans and their liquid, 1 1/2 cups water, and Parmesan rind, if using, and bring to boil. Reduce heat to medium-low and simmer for 10 minutes.

Meanwhile, bring 2 quarts water to boil in large saucepan. Add pasta and 1 1/2 teaspoons salt and cook until pasta is just shy of al dente. Drain. Stir pasta into beans and spread chard leaves on top. Cover, remove from heat, and let sit until pasta is fully cooked and chard leaves are wilted, 5 to 7 minutes. Discard Parmesan rind, if using. Stir in remaining 1 teaspoon rosemary, 1/2 cup Parmesan, and vinegar. Season with salt to taste, and serve, passing extra Parmesan separately.