Boil the pasta: Bring a large pot of salted water to a boil.
Cook pasta until just shy of al dente. Scoop out 1 cup of pasta water, then drain.
Brown the sausage: Heat olive oil in a large skillet over medium-high. Add sliced chicken apple sausage and cook until golden on both sides, 4–6 minutes.
Transfer to a plate.
Sauté aromatics: Lower heat to medium. Add onion with a pinch of salt and cook until translucent, 3–4 minutes. Stir in garlic for 30 seconds until fragrant.
If using, add Dijon and stir.
Deglaze: Pour in wine or broth. Scrape up brown bits and simmer 1–2 minutes to reduce slightly.
Build the sauce: Stir in cream (or half-and-half plus cream cheese). Add thyme and red pepper flakes if using.
Simmer gently 2–3 minutes until slightly thickened.
Add sweetness (optional but great): Stir in diced apple and cook 1–2 minutes to soften slightly. This amplifies the sweet-savory contrast.
Combine: Return sausage to the pan. Add drained pasta and 1/3–1/2 cup reserved pasta water.
Toss until the sauce coats the pasta.
Finish with cheese and acid: Off the heat, stir in Parmesan, lemon juice, and a bit of zest. Season with salt and pepper. If the sauce tightens, loosen with more pasta water.
Serve: Top with parsley and extra Parmesan.
Taste and adjust lemon, pepper, and salt until it sings.