Heat a large, deep skillet or Dutch oven over medium-high heat. Add the Italian sausage, breaking it up with a wooden spoon as it cooks. Brown for 5-7 minutes until no pink remains and it's starting to crisp at the edges.
Add the diced onion to the browned sausage and cook for 2-3 minutes until translucent. Then add the garlic, red bell pepper, dried herbs, and red pepper flakes. Sauté for 1 minute until fragrant.
Pour in the crushed tomatoes and chicken broth, scraping the bottom of the pan to release any browned bits. Bring the mixture to a gentle boil, then reduce to a simmer.
Add the uncooked pasta directly to the sauce mixture. Stir well to ensure all pasta is submerged. Cover and simmer for 8-12 minutes (check your pasta package for timing guidance), stirring occasionally to prevent sticking.
Once the pasta is al dente, stir in the heavy cream (if using) and half of the Parmesan cheese. The sauce should coat the pasta beautifully - if it's too thick, add a splash of broth; if too thin, simmer uncovered for a few more minutes.
Remove from heat and let stand for 2 minutes to allow the sauce to be absorbed further. Sprinkle with remaining Parmesan and fresh basil leaves. Serve immediately for the best texture and flavor experience.