Of all the ways to cook vegetables, there's only one that can achieve perfection with anything from potatoes to collard greens, broccoli to carrots: boiling — or big-pot blanching, as it's called in Thomas Keller's kitchens. "It is probably the best technique anybody can take home,” says Devin Knell, chef de cuisine for Thomas Keller’s restaurant empire. Big-pot blanching is basically boiling, but with serious attention to the finer points: First, the volume of water must be large enough that the food immersed doesn’t cool the water and cause it to drop below the boiling point; second, the water must be salted at a ratio of about one cup per gallon of water, to season the vegetables and help preserve the color; last, as soon as the food reaches perfection, it must be transferred to a large bath of ice water in order to stop the cooking.

“It’s a technique that Keller saw many restaurants doing incorrectly,” says Knell. One of the most common mistakes was too much vegetable dropped into too little boiling water, which, he says, merely steeps the vegetables, producing acids and gasses that discolor the food. Big-pot blanching is also an ideal way to flash-cook leafy greens like kale, chard, and rapini.

In traditional versions of the French stew garbure, all the vegetables get cooked together, creating an undifferentiated mush. Keller’s refined garbure employs blanching — as well as the separate, gentle simmering of carrots and potatoes — to cook each ingredient perfectly and then combine them into one glorious whole. But there’s one point of tradition on which Knell recommends holding firm: “In France, when you get near the bottom of your bowl of garbure, you pour in your remaining wine, mix it all together, and sop it up with bread."

 Spring Vegetable Garbure

(Adapted from Ad Hoc at Home, by Thomas Keller. Serves 8)

Ingredients

  • 3 tbsp canola oil
  • 2 cups thinly sliced carrots
  • 2 cups coarsely chopped leeks
  • 2 cups coarsely chopped yellow onions
  • Kosher salt
  • Freshly ground black pepper
  • Parchment paper
  • 8 cups chicken stock
  • 6 boiling potatoes (a mix of round red and yellow fingerling is good)
  • 2 bouquets garnis (bundles of 3 thyme sprigs, 10 peppercorns, a bay leaf, and a garlic clove, bound together withcheese-cloth)
  • 2 cups cut carrots
  • 1 tsp honey
  • 12 medium asparagus
  • 1 cup green beans, sliced diagonally
  • Cut into thirds, stem ends removed
  • 1 small head of cabbage cut into 6 wedges
  • 1 cup fresh peas
  • 2 cups cooked cannellini beans or other white beans
  • 1 tbsp red-wine vinegar
  • Extra-virgin olive oil
  • Flat-leaf parsley

Step one: Heat the canola oil in an 8- to 10-qt pot over medium heat. Add the thinly sliced carrots, leeks, and onions, and stir to coat in the oil. Season with salt and pepper. Lay parchment paper (loosely cut to size of the pot) on top of the vegetables, pressing it down gently. Cook on low, lifting the parchment and stirring occasionally, for 30-35 minutes, until the vegetables are cooked through but not falling apart. Remove the parchment paper and discard. Add the stock and increase the heat to medium high. Simmer for 20 minutes. Strain the broth into another pot and set vegetables aside.

Step two: Quarter the potatoes and place in a pot with 1 bouquet garni and 2 tsp salt; cover with cold water and bring to a simmer. Simmer potatoes until the tip of a sharp knife will slip easily into the middle (about 10 minutes). Drain and spread on a tray to cool. Put the diagonally cut carrots, honey, second bouquet garni, and a pinch of salt into a medium pot, cover with cold water, and bring to a simmer. Cook for 5 minutes, or until carrots are tender but slightly resistant to the tooth. Drain and discard the bouquet garni.

Step three: Blanch the asparagus. Fill your largest pot with water, adding kosher salt in a ratio of one cup per gallon of water (2 cups for an 8-qt pot). Bring to a rolling boil. Fill another pot or bowl with ice, then add just enough cold water to cover the ice (buying a bag of ice isn’t a bad idea). Meanwhile, remove the tough bottom end of each asparagus. Trim asparagus to the same length and cut into 1-inch pieces on the diagonal. Drop a small handful of asparagus pieces into the boiling water a few at a time:

The trick is to figure out how many you can drop in at once without cooling the water below boiling. Proceed in batches, blanching asparagus for about 1 minute at a time, until bright green and easily pierced with the tip of a paring knife. Using a slotted spoon, transfer to the ice bath for 1 minute to cool, then to a colander to dry. Repeat with the green beans, blanching them for about 2 minutes; the cabbage, about 2 minutes; and the peas, 1 minute.

Step four: Bring the broth back to a simmer; add the carrots, potatoes, and cannellini beans. Stir in the vinegar. Add salt and pepper to taste. Then add all the blanched vegetables and warm just to the desired temperature. Remove from the heat, drizzle extra-virgin olive oil over the top, garnish with parsley leaves, and serve.