For the Caramelized Onions:

1. Cook the Onions:
   • In a large skillet, heat olive oil and butter over medium-low heat.
   • Add the thinly sliced onions and a pinch of salt. Stir occasionally to ensure the onions cook evenly.
   • Sprinkle sugar (if using) to help with the caramelization process. Cook the onions for 25-30 minutes, stirring occasionally until they turn a deep golden-brown color. The longer they cook, the sweeter and richer the flavor will become. Set aside once done.

For the Chilli Oil:

1. Make the Chilli Oil:
   • In a small saucepan, heat olive oil over low to medium heat. Add minced garlic and chili flakes.
   • Let the garlic infuse into the oil, stirring occasionally, for about 1-2 minutes (be careful not to burn the garlic).
   • Add smoked paprika (if using) and salt, then stir to combine. Remove from heat and set aside.

For the Pasta:

1. Cook the Pasta:
   • Bring a large pot of salted water to a boil. Cook the pasta according to the package instructions until al dente, usually about 8-10 minutes.
   • Once cooked, drain the pasta, reserving about 1/2 cup of pasta cooking water.

Assembling the Dish:

1. Combine Everything:
   • In the same skillet used for the onions, add the cooked pasta and toss to combine with the caramelized onions. If needed, add a little reserved pasta water to help the ingredients come together and coat the pasta evenly.
   • Pour the chili oil over the pasta and toss again, ensuring all the pasta is coated with the spicy, flavorful oil.

Serve:

1. Garnish and Serve:
   • Plate the pasta and garnish with chopped parsley and grated Parmesan cheese if desired.
   • Drizzle with extra chili oil if you like more spice, and serve immediately.