A simple, sumptuous vegetable gratin from chefs Ginevra Iverson and Eric Korsh

When we saw this in the Wall Street Journal, we couldn’t wait to try this recipe. Simple maybe, but when we tried it the first time, we found the 30 minute prep time way off the mark. We started cooking at 8 p.m. and didn’t sit down to eat until after 9:30.  We’re loaded with chard again and we’re gonna give this another try because one, it’s delicious and two, we’re pretty fast in the kitchen and we’re determined to get it ready in 30 minutes.

Feb. 14, 2014 12:20 p.m. ET

SIMPLY SUMPTUOUS | As the greens cook, the milk they’re simmering in reduces to a lush, creamy consistency. Ryan Liebe for The Wall Street Journal, Food Styling by Heather Meldrom, Prop Styling by Stephanie Hanes

The Chefs: Ginevra Iverson and Eric Korsh

Ginevra Iverson and Eric Korsh Illustrations by Michael Hoeweler for The Wall Street Journal

What They’re Known For: Elevating bistro classics with a light touch.

ERIC KORSH AND Ginevra Iverson first made this soothing Swiss chard and sorrel gratin, their final Slow Food Fast contribution, during their courtship, more than a decade ago. “We used to cook these long, involved meals at home,” Ms. Iverson said. “Some people go running or to the gym. We did this.” Two restaurants—Restaurant Eloise, in Sonoma County, Calif., and Calliope, in New York City—and two daughters later, this simple gratin remains a fixture in their repertoire. “If you follow the recipe the way it should be done,” Mr. Korsh said, “there is nothing better. It belongs in a museum.”

Thankfully, sticking to the recipe is easy. First, stew the chard and sorrel in whole milk with just a touch of flour until the greens are supple and tender. Then, stir in some Parmesan, pack the creamy leaves into a gratin dish, top with panko and slip the whole thing under the broiler. That really is all that’s required. “Every cook wants to add half and half,” Ms. Iverson said. “They don’t get that this is supposed to be light and about the greens.”

There is a bit of wiggle room when it comes to those greens, however. If you can’t find sorrel at your local market, it’s fine to substitute another leafy green, like kale, in its place, or just use more chard. If it comes to that, toss a little lemon zest into the pot as the greens stew to impart the bright flavor sorrel is known for. Otherwise, just follow the steps laid out below. The recipe has stood the test of time in the Korsh-Iverson household for a reason.

—Kitty Greenwald

Swiss Chard and Sorrel Gratin

Total Time: 30 minutes Serves: 4

3 cups Swiss chard, stems removed, roughly chopped

1 tablespoon butter

3 cloves garlic, thinly sliced

½ pound sorrel, stems removed, roughly chopped

1 tablespoon all-purpose flour

2 cups whole milk

¼ cup grated Parmesan

Salt and freshly ground black pepper

⅓ cup panko bread crumbs

1. Set a heavy pot of salted water over medium-high heat and bring to a rolling boil. Stir in Swiss chard and blanch until softened and bright green, 1-2 minutes. Drain in a colander and squeeze chard leaves to remove excess water.

2. Turn on broiler. Meanwhile, wipe pot clean and set over medium-low heat. Stir in butter and garlic and sauté until garlic lightly browns, about 4 minutes. Increase heat to medium, stir in sorrel and cook until soft, 1-2 minutes. Sprinkle flour over sorrel and cook, stirring, 1 minute more.

3. Add blanched chard to pot with sorrel and stir to combine. Pour in milk and gently simmer, stirring frequently, until liquid almost completely cooks off, about 15 minutes. Remove from heat, stir in Parmesan and season with salt and pepper to taste.

4. Pack simmered greens snugly into a 9-inch round baking dish. Scatter panko overtop and slide dish directly under broiler. Broil until panko turns golden, about 5 minutes. Serve immediately or refrigerate until ready to use, up to 12 hours, and reheat before serving.