Bring a large pot of salted water to a boil. Add the 8 ounces of spaghetti and cook according to package instructions until al dente. Reserve about 1 cup of pasta water before draining.
In a large skillet over medium heat, melt the 1/2 cup of unsalted butter. Add the minced garlic and sauté gently until fragrant and golden, about 1 to 2 minutes. Be careful not to burn the garlic.
Stir in the 2 tablespoons of chili oil and 1 teaspoon of red pepper flakes. Cook for another minute to meld flavors.
Add the drained spaghetti to the skillet and toss to coat evenly. Add reserved pasta water a few tablespoons at a time if the sauce is too thick.
Taste and season with salt as needed. Remove from heat and sprinkle chopped fresh parsley on top. Serve immediately with grated Parmesan cheese.
