In a large skillet, heat olive oil and butter over medium-low heat. Add thinly sliced onions and a pinch of salt, stirring occasionally.

Sprinkle sugar over the onions to aid caramelization and cook for 25-30 minutes or until they turn a deep golden-brown color, stirring occasionally.

In a small saucepan, heat olive oil over low to medium heat. Add minced garlic and chili flakes, stirring occasionally to infuse for 1-2 minutes without burning the garlic.

Incorporate smoked paprika and salt into the infused oil, then stir to combine. Remove from heat and set aside.

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

In the same skillet used for the onions, add the cooked pasta and toss to combine with the caramelized onions. If needed, add a bit of reserved pasta water to help coat the pasta evenly.

Pour the prepared chili oil over the pasta, tossing to ensure every strand is coated with flavor.

Plate the pasta and garnish with chopped parsley and grated Parmesan cheese if desired. Drizzle with extra chili oil for added spice and serve immediately.