Preheat the oven to 400 degrees. Cut off the top ¼ inch of the garlic head to expose the cloves, place on foil cut-side up, sprinkle with salt, and drizzle with 1 teaspoon oil. Wrap in foil and roast until soft and golden brown, about 40 to 50 minutes.

In a large pot, bring salted water to a boil. Finely chop the parsley leaves. Cook pasta according to package instructions until al dente, reserving 1 cup pasta water, then drain.

In a large Dutch oven or skillet, heat the remaining ½ cup oil over medium heat. Squeeze roasted garlic into the oil, breaking it up until fragrant (about 2-3 minutes). Add red-pepper flakes and pepper, then remove from heat to infuse.

Heat garlic oil over medium, then add cooked pasta, ½ cup reserved pasta water, and parsley. Toss constantly, adding more water as needed, until pasta is coated with the sauce.

Serve with extra red-pepper flakes, black pepper, and Parmesan.