In a large bowl or large measuring pitcher, whisk together the butternut squash purée, chicken broth, heavy cream, grated Parmesan, dried sage (or fresh), nutmeg, garlic powder, onion powder, kosher salt, black pepper, and olive oil until the mixture is smooth and well combined. This is your single, pour-over sauce mixture.
Lightly grease the insert of a 6-quart slow cooker with a bit of olive oil or nonstick spray to help prevent sticking.
Place the raw chicken breasts in a single layer on the bottom of the slow cooker. Scatter the sliced onion and minced garlic evenly over and around the chicken.
Add the dry rigatoni on top of the chicken and onions, spreading it out as evenly as possible. Do not stir; you want the pasta mostly on top so it can be surrounded by the sauce.
Slowly pour the entire butternut squash–cream mixture evenly over the raw chicken breasts and rigatoni in the slow cooker, making sure all of the pasta is moistened. Gently press any exposed pasta down with a spoon so it’s just submerged in the liquid. If the pasta isn’t mostly covered, add up to 1/2 cup water to help it along.
Cover the slow cooker with the lid and cook on LOW for 3 1/2 to 4 1/2 hours, or on HIGH for 2 to 2 1/2 hours. Cooking times can vary by slow cooker; begin checking around the earliest time. The chicken is done when it reaches 165°F in the thickest part, and the rigatoni is tender but still holds its shape.
Once cooked, use two forks to shred or slice the chicken directly in the slow cooker, stirring it gently into the creamy butternut squash sauce and pasta. If the sauce seems too thick, stir in a splash or two of warm water or additional chicken broth until it reaches your desired consistency. Taste and adjust seasoning with a bit more salt and pepper, if needed.
Let the pasta sit, covered, for about 5 minutes to allow the sauce to thicken slightly and cling to the rigatoni. The residual heat will help everything meld together.
Serve the creamy butternut squash chicken rigatoni hot, topped with extra grated Parmesan and a sprinkle of chopped fresh parsley or sage, if you like.
Variations & Tips
For a lighter version, swap half of the heavy cream for whole milk or half-and-half; the sauce will be a bit less rich but still pleasantly creamy. If you prefer thigh meat, boneless, skinless chicken thighs work beautifully and stay very tender—just keep the total weight around 1 pound and check for doneness. To add more vegetables, stir in 2 cups of baby spinach or chopped kale during the last 15 minutes of cooking on LOW (or last 5–10 minutes on HIGH); the greens will wilt into the sauce without becoming mushy. You can also tuck 1 to 2 cups of small broccoli florets or frozen peas around the chicken before adding the pasta for extra color and texture. For a smokier profile, add 1/4 teaspoon smoked paprika to the sauce mixture. If you enjoy a stronger sage note, finish the dish with a drizzle of sage-infused brown butter: quickly brown 2 tablespoons butter with a few fresh sage leaves in a small pan and pour over the pasta just before serving. Leftovers reheat well with a splash of water or broth to loosen the sauce; the pasta will continue to absorb liquid, so don’t hesitate to add more as you warm it on the stovetop or in the microwave.
