Add pasta and water to a pot. Cover and bring to a boil.
As soon as water begins to boil, turn heat down to low to prevent the water from boiling over. Set a stopwatch. Give the pot a stir every other minute to prevent pasta from sticking to the bottom, but otherwise keep the lid on.
At the 5-minute mark, mix in your spinach or broccoli if using.
Simmer for a further 5–10 minutes (depending on how done you like your pasta), then turn off the heat. Stir in the pesto and add salt to taste (see Note 2).
Notes
For one or two servings of pasta, use the ratio in the recipe above. If cooking more servings, reduce the water to be twice the amount of dried pasta by weight. For example, if you want to triple this recipe to make three servings of pasta, use 9oz dried pasta (255g) and 18oz water (510g).
I add 1/8 tsp of salt. You may need to add more or less depending on which pesto you are using. Keep in mind we are not draining the water from this pasta so you can't salt the pasta water as generously as you usually would.