01 - Boil fettuccine in salted water until al dente. Reserve 1/2 cup pasta water before draining.
02 - Heat olive oil and butter in skillet over medium heat. Add onions and salt, cook 10 minutes until softened and lightly browned.
03 - Sprinkle brown sugar over onions. Continue cooking 15-20 minutes, stirring frequently, until deeply golden and caramelized.
04 - Add garlic and red chili to caramelized onions. Sauté 1-2 minutes until fragrant.
05 - Stir in honey, heavy cream, Parmesan, red pepper flakes, and black pepper. Simmer 2-3 minutes until slightly thickened.
06 - Add cooked fettuccine to skillet. Toss thoroughly, adding reserved pasta water as needed for desired consistency.
07 - Adjust seasoning to taste. Serve hot with fresh parsley and additional Parmesan.