01 - Cook fettuccine in large pot of salted boiling water until al dente. Reserve 1/2 cup pasta water, drain and set aside.
02 - Heat olive oil and butter in large skillet over medium heat. Add sliced onions and salt. Cook stirring occasionally until softened and beginning to brown, approximately 10 minutes.
03 - Sprinkle brown sugar over onions and continue cooking, stirring frequently, until deeply caramelized and golden, 15-20 additional minutes.
04 - Add garlic and red chili pepper to caramelized onions. Sauté 1-2 minutes until fragrant.
05 - Stir in honey, heavy cream, Parmesan, red pepper flakes, and black pepper. Simmer gently 2-3 minutes until slightly thickened.
06 - Add cooked fettuccine to skillet. Toss thoroughly to coat, incorporating reserved pasta water one tablespoon at a time until desired consistency achieved.
07 - Taste and adjust seasoning as necessary.
08 - Serve hot, garnished with fresh parsley and additional Parmesan cheese.