Bring a large pot of salted water to a boil. Cook the pasta according to package instructions until al dente. Reserve ¼ cup of pasta water, then drain the pasta and set aside.
While the pasta cooks, heat olive oil or butter in a large skillet over medium heat. Add the sliced onions and a pinch of salt. Cook for 8-10 minutes, stirring occasionally, until the onions are soft, golden, and caramelized. (If the onions start to stick, add a splash of water to deglaze the pan.)
Add the minced garlic to the skillet and sauté for 1 minute until fragrant.
Stir in the gochujang, soy sauce, red chilli flakes, parmesan and honey (or sugar). Cook for 1-2 minutes, allowing the flavors to meld together.
Reduce the heat to low and add the heavy cream. Stir to combine, creating a creamy, spicy sauce. If the sauce is too thick, add a splash of the reserved pasta water to loosen it.
Add the cooked pasta to the skillet and toss to coat evenly in the sauce. If needed, add more pasta water to achieve your desired consistency.
Stir in the chopped parsley and drizzle with 1-2 tbsp of chili oil (adjust to your spice preference). Toss everything together.
Garnish with extra chopped parsley, a drizzle of chili oil, and a sprinkle of sesame seeds (if desired). Serve immediately!
