100g pasta
60g pesto
pasta water, one tbs at a time, as needed.

Cook according to normal instructions. See them here.

Mix pesto and pasta off of heat. Otherwise the cheese in the pesto will melt and separate.

Add pesto to a mixing bowl.

Add drained pasta and mix.

Add a little pasta water to loosen the pesto sauce until it changes from a paste to a creamy sauce. Stir stir stir.