Cooking Time

The recipes on this site were developed with the SousVide Supreme, a very capable cooking device which uses water convection. More recently, we’ve been cooking with immersion circulators which maintain even cooking temperatures by moving water in the bath with a pump. If you’re using an immersion circulator, slightly reduce cooking times for best results.

Caramelized Onions and French Onion Soup

Caramelized Onion

A recent cold and rainy day got me in the mood for French Onion Soup, so I went straight to Thomas Keller’s recipe in his Bouchon cookbook. After close to 7 hours of stirring and watching the onions as they developed the perfect caramelization, I proceeded to make his wonderful version of the bistro classic.

The long process reminded me why I don’t make French Onion Soup more often! As an alternative, the onions can be caramelized in a slow cooker for 10-plus hours, however all those hours of the onion aroma wafting through the closed-up house put me off that idea. And nary a restaurant in my area can make a version as good as homemade.

Still, I simply love this comforting, delicious winter potage, so I set out to use the sous vide method to bring out the ultimate sweetness of the onion as well as eliminate the hours of onion smell and the fuss of “watching the pot.”

My first experiment proved to me that sliced onions emit a great deal of gas. I sliced the onions, added a bit of butter and sea salt, vacuum sealed the pouches, then dropped them in the water oven and waited. After about an hour, the SousVide Supreme’s lid started rising and I could see that the gases had released from the onions, expanding the bags.

Despite this disconcerting behavior, everything looked okay, so I gently placed a cast iron pan on the lid and waited the full 15 hours until the onions were done. Then when I lifted the lid, I found that two of the three bags had opened from the pressure of the gas. Luckily, the third bag kept its seal and contained lovely brown onion slices in their own juices. After about 30 minutes in a saucepan, they caramelized to a beautiful, rich, golden molasses color.

I was simply elated with the end result, but I needed to remedy the compromised vacuum bags. Next day I tried again, and this time I simply double bagged the onions. They were perfect.

Caramelized Onions

Makes approximately 1 cup

large sweet yellow onions
tablespoons unsalted butter, diced, then divided into 3 equal portions
Sea salt

  1. Preheat the water bath to 200ºF (93°C).
  2. Remove the tops and bottoms from the onions and cut them in half lengthwise. Remove the peels and any bruised outer layers. With a small knife, carefully cut a V wedge in each of the halves to remove any core. This should be only a small portion of the center.
  3. Place the cut half of the onion face down on a cutting board with the large root end facing toward you. Cutting with the grain, carefully slice the onion lengthwise into ¼-inch slices. Repeat with each onion half until you have sliced all 4 onions.
  4. Prepare 6 large bags for the water bath, 3 of them about 10 inches long, the other 3 about 12 inches long. Three of the bags will contain the onions. The 3 longer bags will be for double bagging.
  5. Transfer the sliced onions to paper towels or a clean dish towel and gently pat them, eliminating as much of their exuded moisture as possible. Working quickly, divide the onions equally between the 3 smaller bags. Add a butter portion and a pinch of sea salt to the onions in each of the 3 bags. Immediately vacuum seal the bags.
  6. Now place each of the sealed bags into 1 of the larger bags, folding down the top of the sealed bag inside the second bag. Vacuum seal the outer bags. Put the 3 double bags in the water bath. Set a heavy pan on top of the lid of your water oven in case the gases cause the bags to rise (at some point during cooking the gases will dissipate).
  7. Cook for 15 hours. At this point, the onions will have exuded all of their liquid, cooked down to a soft consistency, and turned a medium-brown color. Remove the bags from the water oven and open carefully.
  8. Place the onions in a fine mesh strainer set over a bowl (reserve the strained juices to add to the stock if making soup). Transfer the strained onions to a medium-size heavy-bottomed or enameled saucepan. Cook over medium-high heat for about 15 minutes, or until all the liquid has evaporated, stirring with a wooden spoon and watching them closely so they do not burn. Continue cooking until the onions caramelize and darken to a golden molasses color, about 15 minutes more.

The caramelized onions will keep in the refrigerator for 2 days or can be frozen for up to a month. This recipe can be doubled.

French Onion Soup

French Onion Soup

Serves 2

cups beef stock, preferably homemade, or high-quality, low-sodium beef broth (Perfect Addition offers beef, chicken, veal, and fish stocks in 16-ounce frozen containers)
Reserved juices from the cooked onions
Caramelized onions
teaspoon all-purpose flour
Splash of sherry vinegar
Sea salt and freshly ground black pepper
croutons made from day-old French bread, each cut 3 inches in diameter and ¼-inch thick, brushed with olive oil on both sides, and broiled to a golden brown color (can be made several hours ahead)
ounces Comtė, Emmentaler, or Gruyère cheese, cut into 4 slices, each about 5 by 5 inches (or large enough to overlap wide-mouth soup bowls or tureens by ½ inch) and ¼-inch thick. Grate the leftover cheese for topping; grated cheese browns better under the broiler

  1. Place the beef broth and reserved onion juices in a saucepan large enough to accommodate the liquid and heat over medium-high heat until just boiling. Remove from the heat.
  2. Place the caramelized onions in a large saucepan over medium-high heat and add the flour, stirring constantly until it is incorporated into the onions. Continue to cook and stir for another 1 or 2 minutes. Add the heated stock and the vinegar to the onion-flour mixture and simmer for about 30 minutes. Season with salt and pepper to taste.
  3. Preheat broiler to high. Place a piece of aluminum foil on a baking sheet large enough to accommodate the soup bowls or tureens. Place the bowls on the baking tray and fill with the soup to within ½ inch of their tops. Place 2 of the prepared croutons on top of the soup in each of the bowls, then cover them with 2 of the cheese slices, overlapping the rims of the bowls or tureens by about ½ inch. Cover the entire surface of the bowls with grated cheese.
  4. Broil for 2 to 3 minutes, or until the cheese bubbles and browns, forming a crust, checking often to make sure that the cheese does not burn. Serve hot.

6 comments to Caramelized Onions and French Onion Soup

  • Since I don’t have a vacuum sealer, I use the ziplock bags with the simple plastic pump to remove air. I wonder if the ziplocks would be ideal for this application because you could pump the gas out of the bags part of the way through.

    How far along in the process did the gas appear?

    I’ve enjoyed your recipes for several months. Thanks so much for taking the time to share your wonderful sous vide work!


    • Interesting thought about using the pump to expel gas during cooking, Wayne. I wonder if you’d be asphyxiated in a cloud of onion gas?! My tinkerer husband immediately started talking about setting up some sort of dryer-exhaust hose to pump the gas outside…

      Seriously, though, Sally reports that the bags expanded with gases about an hour or so into cooking. Want to give your method a try and report back? I’m curious about your results with ziplocks and the pump in general — I got spooked the one time I tried them, as I had a leak and ended up with waterlogged fish. Pam’s not had any issues, though. How’s your luck been so far?

      Thanks for the kind words. Much appreciated.

      • I’ve had a rather good experience with the ziplocks and pump, with success probably better than 95% of the time. I think that you really have to watch as you pump the air out to make sure that no liquid arrives in the area of the valve because I think it’s when liquid gets into the valve that it no longer seals reliably.

        You probably couldn’t just pump gas out half way through – rather, you’d have cook for an hour, then remove the onions, take them outside to release the offending fumes, then transfer to another bag and reseal with the pump. This is the only way I can think of that would sidestep the issue of liquid entering the seal.

        Doing so would mean using two bags total, so the only advantage I can think of is that the onions could still be immersed after being sealed the second time.

        Now, for a delicate question … Prior experiences with French Onion Soup have led to a human gastric phenomenon much like the one you describe happening in the plastic bags with the concomitant risk of explosions and toxic fumes. I’m wondering if cooking the dish in this way has removed some of these unpleasant postprandial events which have been known to ordinarily accompany the consumption of this delectable delight to the point of shutting down polite dinner parties?

        • Good tip on using the pump; thanks. Since my experience with “pump failure” was with a dish that had a fair amount of liquid, I bet that’s exactly what the problem was.

          Except for the issue with the possible broken seal due to the gas pressure (is that the right term?), I think Sally’s solution to double bag and then put a weight on the water oven lid is probably the easiest. The gas does dissipate during the time the onions are in the water bath, so we’re spared any olfactory unpleasantness, too! As to where it goes…?

          Gee, wouldn’t it be great if sous vide was also a solution for farts! Alert the SousVide Supreme marketing team! LOL.

  • Terrence

    Maybe you should use these bags in the future.

    They’re zip bags that you can periodically take out to release the air. This would prevent the bags from exploding.

    • Very practical, if not as dramatic. We’ve tried the new SVS branded bags, introduced since this recipe was posted, and think the quality is excellent. They’re pricey, but you get what you pay for, eh?