Prepare pasta according to package directions. Carefully reserve one cup of the pasta water to use in the sauce.
Over medium-high heat, add all but 2 tablespoons of the cream to a saute pan or skillet. When it bubbles, add the salt.
Small bubbles will erupt into larger bubbles. Stir.
When the sauce thickens enough to cover the back of a spoon or leaves a clean line in the bottom of the pan when you pull a spatula across it, add the pasta water. Cook over medium-high heat for about 3 minutes, until it bubbles again and the sauce thickens.
Add the reserved 2 tablespoons of cream, and heat through. Add the cheese, garlic (if using) and a few cranks of pepper. Taste, and add more salt if needed.
Add the cooked pasta and any additional ingredients and stir well to coat.