Step 1: Brown and Drain the Sausage - Place a large skillet over medium heat and add the Italian sausage. Break it into small pieces with a wooden spoon as it cooks so there are no oversized chunks hiding in the finished pasta. Continue cooking until the sausage is browned and no pink remains. Drain away the extra grease before transferring the sausage to the slow cooker. This quick step gives the meat better texture and keeps the final sauce from becoming oily.
Step 2: Add the Aromatics and Seasonings - Add the salt, black pepper, diced onion, and minced garlic to the slow cooker with the browned sausage. Give everything a quick stir so the onion and garlic are spread throughout the meat. As the mixture cooks, those small pieces of onion will soften and become sweet, while the garlic will perfume the entire sauce.
Step 3: Pour In the Broth and Cream - Pour the chicken broth and heavy cream over the sausage mixture. Stir gently, scraping along the bottom and sides so all the ingredients are sitting in the liquid. The broth will eventually help cook the pasta, while the cream gives the sauce the rich body that makes this meal feel especially comforting.
Step 4: Add the Boursin and Italian Seasoning - Place both rounds of Boursin cheese into the slow cooker, then sprinkle in the Italian seasoning. You do not need to break the cheese apart or whisk it smooth at this stage. It will soften slowly as the sauce heats. Stir just enough to settle the cheese into the liquid, then put the lid on the slow cooker.
Step 5: Slowly Cook the Sauce - Cook the sauce on low for two and a half to three hours. Try to leave the lid closed during this stage, since opening it releases heat and can extend the cooking time. The onion will soften, the garlic will mellow, and the Boursin will become warm enough to blend easily into the broth and cream.
Step 6: Stir the Sauce Until Smooth - Remove the lid and stir the mixture thoroughly. Press any remaining pieces of Boursin against the side of the slow cooker with your spoon until they melt into the liquid. The sauce should look smooth, creamy, and evenly combined. Do not worry if it seems a little thinner than you expect, since the pasta will absorb some of that liquid as it cooks.
Step 7: Add and Submerge the Pasta - Pour the uncooked penne directly into the sauce. Stir carefully until the pasta is evenly distributed and every piece is sitting below the surface of the liquid. Submerging the pasta is important because any pieces left sticking out may cook unevenly or stay firm.
Step 8: Cook the Pasta Until Tender - Cover the slow cooker and switch the heat to high. Cook for thirty to forty five minutes, stirring once or twice during that time. Begin checking the pasta around the thirty minute mark, since different slow cookers can vary quite a bit. You want the penne tender but not mushy, with enough structure left to hold the creamy sauce.
Step 9: Melt In the Parmesan - Once the pasta is tender, add the shredded Parmesan cheese. Stir slowly until it has melted completely and the sauce looks thick, glossy, and creamy. If the pasta seems thicker than your family prefers, add a small splash of warm chicken broth and stir again until the sauce loosens.
Step 10: Garnish and Serve - Sprinkle the chopped parsley over the top just before serving. I like to spoon the pasta into shallow bowls while it is still hot, making sure everyone gets plenty of sausage and sauce. Add a little extra Parmesan at the table and serve it right away, when the sauce is at its creamiest.