01 - Boil pasta in a large pot of salted water until al dente. Reserve 1/2 cup pasta water, drain, and set aside.
02 - Heat 1 tablespoon olive oil in a large oven-safe skillet over medium heat. Add sausage, crumble it with a spoon, and cook for 7 to 8 minutes until browned and fully cooked. Transfer sausage to a plate.
03 - Set oven to broil function, or preheat to 450°F.
04 - Add remaining 1 tablespoon olive oil and 1 tablespoon butter to skillet. Add apple slices and onion. Season with salt, pepper, and thyme. Sauté for 5 to 7 minutes until apples are golden and onions are tender.
05 - Add minced garlic and sauté for 1 minute until fragrant.
06 - Return sausage to skillet. Add cooked pasta, chicken broth, and reserved pasta water as needed for a silky sauce. Stir in spinach until wilted.
07 - Dot the mixture with remaining 1 tablespoon butter and sprinkle Parmesan cheese evenly over the top.
08 - Place skillet under broiler for 2 to 3 minutes until the top is golden and bubbly.
09 - Serve immediately with additional Parmesan and red pepper flakes, as desired.