Bring a large pot of water to a boil. Add 1 tbsp kosher salt and the rigatoni. Cook until al dente according to package directions. Reserve 1 cup of pasta water, then drain and set aside.

While pasta cooks, heat a large, deep skillet over medium-high heat. Add sausage (breaking it into crumbles) and cook until browned and no longer pink, reaching an internal temperature of 160°F (71°C), about 6-8 minutes. Transfer to a plate, leaving any rendered fat in the skillet.

In the same skillet, reduce heat to medium. Add garlic and red pepper flakes (if using), sauté for 1 minute until fragrant. Stir in sun-dried tomatoes and cook 2 minutes. Pour in heavy cream and chicken broth, scraping up any browned bits. Simmer gently for 3-4 minutes until slightly thickened.

Add the chopped kale to the sauce, stirring until wilted, about 2 minutes. Return sausage to the skillet. Add the drained pasta and 1/4 cup reserved pasta water. Toss everything together, adding more pasta water if the sauce seems too thick. Stir in Parmesan cheese until melted. Season with salt and pepper to taste.

Divide the pasta among bowls, garnish with extra Parmesan and fresh basil if desired. Serve immediately.