This simple trick can turn jarred tomato sauce and dry spaghetti into a restaurant quality meal.

By Julia Sklar
August 30, 2019
Photo: Alison Miksch; Styling: Caroline M. Cunningham

Eating pasta at a restaurant can feel like such a luxury. The pasta has some bite to it and the sauce is thick, glossy, and creamy—sometimes even without the help of dairy—and seems to effortlessly cling to the pasta, as if beholden to an “if it goes, I go” pact as you slurp up noodles.

Back at home, the same meal can feel like a sad emergency dinner, as you twirl spaghetti around your fork, and watch watery, lifeless sauce drip off the strands and plunk back down on the plate. By the end, you’ve eaten forkfuls of mostly bare pasta, and are left with a sea of extra sauce.

It’s tempting to think that restaurants can one-up you because they’re feeding you homemade sauces that have been simmering for hours and that are destined to adorn handcrafted noodles whose dough was deftly kneaded just moments before you arrived. While it certainly doesn’t hurt to start with topnotch base ingredients, the real secret to the marriage of these two elements actually lies in a technique called emulsifying, and you can replicate it at home to transform boxed pasta and jarred sauce all the same.

WATCH: What’s the Difference Between Pasta Sauce and Pizza Sauce?

An emulsion is a scientific concept that simply means at least two liquids that normally won’t mix have been forced to come together. In the world of food, you might already recognize this concept in the difference between repellant oil and vinegar on the one hand, and a thick, creamy vinaigrette on the other. The latter, which somehow contains both oil and vinegar and yet doesn’t seem to separate right away, is an emulsion.

There are three absolutely vital steps to emulsifying any kind of pasta sauce: reserving some pasta water, introducing fat slowly, and providing some kind of agitation—which in this context means lots of stirring/mixing/flipping, not general frustration with the state of the world (although cooking is a great outlet for that, too).

In greater detail, the process would look like this for a single serving of boxed spaghetti and jarred marinara:

  1. Before you do anything, make sure you have some butter in the fridge—and leave it there. (Fridge-cold Earth Balance works equally well as a non-dairy substitute in this context.)
  2. Next, bring heavily salted water to a boil in a two-quart pot.
  3. Add 3 ounces of your spaghetti of choice (in lieu of a kitchen scale, this is about the diameter of a quarter, if you scrunch your hand around a bundle of dry noodles), and cook just until you’d actually consider the pasta a bit underdone. You’ll know it’s there if you take a little bite and see a tiny dot of white in the center where the pasta isn’t quite finished cooking. The rationale behind this is: The pasta will keep cooking in the sauce later. So if you pull it out of the water at a ready-to-eat consistency, by the time you’re done mixing everything together, it will actually be overcooked.
  4. Before draining the pasta, reserve at least half a cup of the water it cooked in. This water, plus the starch left behind from the boiling pasta, can act as a handy glue for finishing sauces. It’s hard to know if you’ll need it at this stage, but you can’t get it back once it’s down the drain, so we set some aside now to do our future selves a solid.
  5. In the now empty pot that you cooked the pasta in, toss in about half a cup of your preferred brand of tomato sauce. This will be just enough to cover the pasta without drowning it in sauce. Bring the sauce to a gentle simmer. The bubbles will help with all that agitating we’re gearing up to do.
  6. Remember the cold butter in the fridge? Time for it to shine—literally. Take it out of the fridge, and add half a tablespoon of butter to the sauce, stirring constantly. The very cold butter will combine with the simmering sauce as it slowly melts. Keep adding half tablespoons of butter until the sauce is thick enough that you can run a spoon through it and see all the way to the bottom of the pot without the sauce quickly seeping back to fill the gap. Depending on how watery or thick your jarred sauce is, the amount of butter you’ll need to add will vary, but don’t exceed 2 tablespoons. You’ll also know you’ve hit the spot if you look closely at the sauce and notice tiny glistening beads of fat evenly distributed throughout. It shouldn’t look like a layer of melted butter floating on top of tomato sauce.
  7. When the sauce is ready, add back your drained pasta directly to the pan and mix vigorously. The mixing motion will further emulsify and thicken the sauce by pulling in bits of starch from the pasta—mixing pasta and sauce directly in the pan, rather than pouring sauce over a plate of pasta, is a crucial finishing step for that restaurant quality you’re looking for. Different types of pasta mingle with sauces differently—some will soak up more of the liquidy bits than others, so you’ll want to use your eyes to see if the sauce is the thickness you want it to be. If you find that your sauce is too thick, this is where you can add some of the reserved pasta water back, little dribbles at a time. If you over-water and the sauce becomes too thin, just let some of it cook off and you’ll see the sauce thicken up again. It’s pretty resilient to fumbles at this stage.

In the end, it’s the gradual combination of fat, starch, and acid (in this case from the tomatoes) that build a cohesive dish where there were formerly disparate ingredients that wouldn’t have hung out or clung together if quickly combined. This same basic order of events can be repeated with any sauce. If you’re eager to try this with a homemade sauce, the easiest place to start is a simple aglio e olio (garlic and oil). Slowly heat some slices of garlic in olive oil, along with other aromatics you like, such as freshly ground black pepper or spicy red pepper flakes, then mix in the cooked pasta, and slowly pour in reserved pasta water as you aggressively stir it all together. You’ll see the sauce start to thicken and come together as you stir.

And if you really want to take things to the next level, even with the jarred sauce, take the combined pasta and sauce off the flame and sprinkle in teaspoons of Parmesan at a time, each one followed by a splash of pasta water, stirring vigorously to melt and combine the cheese. The gradual combination of Parmesan and pasta water is the principle behind the cult favorite cacio e pepe, the queen of emulsified sauces, and which you’re now totally capable of trying your hand at.

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