1 pound uncooked mild Italian sausage, casings removed
3 tablespoons unsalted butter, divided
1/2 cup finely chopped onion
1 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
1 clove garlic, minced
1 tablespoon tomato paste
1 (28-ounce) can crushed tomatoes
2 to 3 cups water or low-sodium chicken broth
1 tablespoon apple cider vinegar
2 teaspoons granulated sugar
1 teaspoon dried oregano
8 ounces dry O-shaped pasta (2 cups), also known as anelli or anelletti
For serving: Parmesan cheese, red pepper flakes
Divide the sausage into 32 (1/2-ounce) portions and roll each one into a tablespoon-sized meatball.
Melt 2 tablespoons of the butter in a 10-inch high-sided skillet over medium-high heat. Add the meatballs and cook, turning occasionally, until browned all over, about 3 minutes per side. The meatballs might not be completely cooked at this point. Transfer to a plate.
Return the pan to medium-high heat and melt the remaining 1 tablespoon of butter. Add the onion, salt, and pepper, and cook, scraping the browned bits from the bottom of the pan, until the onion softens, about 5 minutes. Stir in the garlic and tomato paste and cook for 1 minute. Pour in the tomatoes, 2 cups of the water or broth, vinegar, sugar, and oregano. Stir in the pasta and meatballs, along with any juices that have accumulated on the plate. Bring to a boil.
Reduce the heat to medium-low and simmer, stirring occasionally, until the pasta is al dente and the meatballs are cooked through, 25 to 30 minutes, adding more water or broth as needed if you want a soupier consistency. Ladle into bowls and top with Parmesan cheese and red pepper flakes, if desired.