Bring a large pot of generously salted water to a boil. Add ditalini and cook to al dente (usually 1–2 minutes less than package directions). Drain and set aside.

While the pasta cooks, heat 1 tablespoon oil in a large skillet over medium-high heat. Add the ground sausage and break it up with a spatula. Brown for 6–8 minutes until nicely caramelized. Drain excess fat from the pan, leaving a little for flavor.

Reduce heat to medium. Add the diced onion to the skillet and cook until soft, about 3–4 minutes. Stir in the minced garlic and cook until fragrant, about 30–45 seconds.

Push the meat and aromatics to one side, add the tomato paste and cook for 1–2 minutes, stirring frequently to deepen the tomato flavor.

Pour in the chicken broth and use a wooden spoon to scrape up the browned bits from the pan. Let the mixture simmer for 3–4 minutes so the liquid reduces slightly.

Lower the heat and stir in the heavy cream. Add the grated Parmesan and whisk until the sauce is smooth and slightly thickened.

Season with kosher salt, cracked black pepper, and red pepper flakes (if using). Fold in the cooked ditalini so pasta is evenly coated.

Heat briefly just until everything is warm. Serve immediately with extra Parmesan on the side.