Step 1
Place sausage in an oven-safe skillet over medium heat. Poke holes into the sausage with a fork. Cook turning as needed until browned and firm 5 to 7 minutes. Transfer to a plate and let cool to room temperature.
Step 2
Preheat the oven to 400 degrees F (200 degrees C).
Step 3
Season chicken breasts with salt pepper and cayenne. Refrigerate sausage until ready to use.
Step 4
Heat oil in the same skillet over medium-high heat. Sear chicken breasts skin-side down until browned 5 to 6 minutes.
Step 5
Meanwhile cut off the base of the mushrooms and separate individual segments. Dice cold sausage.
Step 6
Flip chicken breasts over and sear on the opposite side 2 to 3 minutes more. Set aside on plate.
Step 7
Add red onion sausage and mushrooms to the skillet. Season with salt. Cook and stir until mixture begins to brown about 5 minutes. Turn off heat and return chicken to the skillet skin-side up.
Step 8
Bake in the preheated oven until chicken is no longer pink in the center and the juices run clear about 15 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).
Step 9
Transfer chicken to serving plates. Cover skillet handle with a towel; place over high heat. Cook and stir sausage mixture until caramelized about 1 minute. Pour in wine and simmer until reduced by about half about 2 minutes. Reduce heat to low and toss in butter and 1 tablespoon parsley. Stir frequently until butter melts.
Step 9
Spoon sauce over the chicken. Garnish with remaining parsley.