Bring a large pot of salted water to a rolling boil. Add pasta and cook until al dente (8-10 minutes). Reserve 1 cup of pasta water, then drain.

Heat 2 tablespoons olive oil in a large skillet over medium heat. Add sliced onions and salt. Sauté for about 10 minutes until they soften.

Add sugar to the onions and cook for an additional 15-20 minutes, stirring frequently until they caramelize to a deep golden brown.

Reduce heat and add minced garlic to the skillet. Sauté for 1-2 minutes until fragrant.

Lower heat, add drained pasta, and toss to coat with onions and garlic, gradually adding reserved pasta water to reach desired consistency.

Drizzle remaining olive oil and chilli oil over pasta mixture. Season with black pepper and toss again to combine evenly.

Serve warm, garnished with grated Parmesan cheese and chopped parsley.