Pasta Water Is the Secret to Superior Sauce
Don't throw the water out after your pasta is cooked. It's a simple thing, but it might feel like a revelation. If you haven't heard this cooking motto before, consider adapting to it now. The water left in the pot after you have cooked your spaghetti, fusilli, or shells is loaded with the starch the pasta left behind, which is why it looks cloudy.
A small amount of this water can really enhance your pasta dishes. It works as a binder and a thickener: A skillet of vegetables, pancetta and eggs, or just garlic and butter can be turned into a silky sauce for pasta with the addition of a cup or two of starchy cooking water.
When to Use Pasta Water
Pasta water works best when added to sauce made in a pan—that means noodles enjoyed with marinara sauce or Bolognese don't really have a need for the starchy cooking water. But should you find that your sauce is too thick, or that it isn't clinging to your pasta enough, instead of adding more oil use a little pasta water to thin it out. Knowing when to use pasta water just takes a bit of training. Think a step ahead: Catch yourself before you drain the pasta in a colander, and ladle a cup or two of water from the pot. Even more efficient is the professional cook's technique: Skip the colander and scoop the cooked pasta with a mesh spider directly from the pot into a waiting skillet.
To set up for this restaurant-like method, follow these simple steps: While your pasta water is coming to a boil, create the base of your sauce in a large skillet. Melt butter or heat olive oil, and cook onions, garlic, or other soffrito. This is also the point at which you would cook sausage or cured meats, such as pancetta, guanciale, or bacon, rendering the fat and browning the meat.
Next you'll build another layer of flavor: Add any vegetables that you're including. Give them space in the pan if they need it. Mushrooms don't like to be crowded and should be cooked in batches, whereas dark, leafy greens can be piled on top of each other and tossed as they cook and wilt down into a smaller amount.
Very Al Dente Is Key
When the pasta is al dente—or even less cooked than that (we subtract as much as three minutes from the cooking instructions on the pasta box), add it to the pan with the vegetables. Stir in a cup of the hot pasta water, and toss everything together until well combined. Add more cooking water as needed, up to about two cups for each pound of pasta, until it's all coated and the sauce begins to emulsify. The pasta will continue to cook a little bit while you do this, even if the heat is turned off but that's okay because you've taken it out of the water early. While the pasta is in the skillet with all the other ingredients and the pasta water, an amazing thing is happening: It's absorbing the flavors you've developed, creating a luscious, savory sauce, meaning the whole is becoming greater than the sum of its parts.