Heat olive oil in a 12-inch skillet or Dutch oven over medium-high heat. Add the sausage and cook, breaking it into small pieces with a wooden spoon, until browned and cooked through, about 5-7 minutes. Use a slotted spoon to transfer the sausage to a plate, leaving the rendered fat in the pan.

Reduce heat to medium. Add the diced onion and cook, stirring occasionally, until softened and translucent, about 4 minutes. Stir in the garlic and red pepper flakes (if using) and cook for 30 seconds until fragrant.

Add the tomato paste and stir constantly for 1 minute, letting it darken slightly and caramelize. Pour in the white wine (or broth) and scrape up any browned bits from the bottom of the pan. Let it simmer until reduced by half, about 1-2 minutes.

Pour in the chicken broth and bring to a boil. Add the rigatoni, stirring to ensure all pasta is submerged. Return to a boil, then reduce heat to a vigorous simmer. Cook, stirring occasionally, until the pasta is al dente and most of the liquid is absorbed, about 10-12 minutes. Stir more frequently toward the end to prevent sticking.

Remove the pan from the heat. Add the cream cheese cubes and stir until completely melted and incorporated into the sauce. The sauce should look creamy and coat the pasta nicely.

Return the cooked sausage to the pan, along with the Parmesan cheese. Stir until the cheese is melted and everything is well combined. Taste and season with salt and black pepper as needed. The Parmesan adds salt, so go easy.

Serve immediately, garnished with fresh parsley and extra Parmesan. For best texture, eat right away—the sauce thickens as it cools.