Burger Friday: Bison and mushrooms make for a winning combo at Marin Restaurant & Bar in Minneapolis

The burger: Fans of mushroom burgers will want to hightail it to Marin Restaurant & Bar, because chef Mike Rakun just dropped a whopper on his menu, and it might not be around forever.

Inspiration came from social media. And the James Beard Foundation.

In May, the culinary organization tossed out a challenge to chefs: Come up with a "delicious, healthy and sustainable" burger that incorporates finely chopped mushrooms into the patty's ground meat (following at least a 25 percent mushroom/75 percent meat equation), offer it through July 31 and encourage diners to share photos of the results on Instagram, using the hashtag #BetterBurgerProject.

Fun, right? It's also a win-win. Diners across the country get a crack at a good and good-for-you burger, and the top five vote-getting chefs earn a trip to New York City and the opportunity to prepare their iteration for all kinds of food industry bigwigs at the James Beard House.

Rakun's participation in the contest was serendipitous.

"I was just screwing around on Instagram, and it just popped up," he said. "It's right up our alley, so I started to fiddle around."

Lucky us, because all that tinkering yielded a winner. At least in my book. Instagramers will determine the actual victor.

At Mill Valley Kitchen, Marin's four-year-old sibling in St. Louis Park, Rakun featured both bison burgers and grass-fed beef burgers on the menu. But after two years, "We crossed our fingers and pulled the beef burger off the menu," he said. "I was nervous about it, because we would sell almost equal amounts of each one. But almost no one batted an eye. People just went for the bison."

The bison hails from a co-op of South Dakota family farms. Rakun prefers it because of its slightly higher fat content.

"It's a grain-finished product," he said. "It appeals to people more than the 100-percent grass-fed meat. Bison is already so naturally lean, which leaves a very slim margin of error. With this product, we've been able to convert a lot of people from beef to bison."

The recipe is simplicity itself. Rakun sautés meaty, Minnesota-cultivated shiitakes with flavor-boosting garlic, shallots and thyme. The mixture is cooled and then folded into the ground bison. "A little salt and pepper, and away she goes," he said.

Despite bison's lean nature, this is a remarkably juicy patty. The mushrooms help, of course, but so does the somewhat novel -- for burgers, anyway -- cooking process. Rakun bakes the patties in the kitchen's high-heat, hardwood-burning oven.

In order to accentuate that mouth-watering meat-mushroom flavor, Rakun wisely keeps the garnishes to a minimum: Snappy bread and butter pickles, tangy pickled ramps, a swipe of a slightly smoky ramp-infused mustard and peppery sprigs of nutrient-rich watercress. Perfect.

"It's all fitting for the season," said Rakun. "It's spring, and the cress is overflowing right now. I was up to my ears in ramps, we had a hundred-plus pounds of them. That ramp mustard is great on everything." I bet. He should bottle it and get it on store shelves.

As for the bun, two thumbs up. Rakun tapped Turtle Bread Co. to produce it especially for the restaurant, a tasty multigrain-er that's fortified with millet, flax and sunflower seeds. It's a welcome change from the monochromatic white-bread buns that dominate Burger World.

Rakun said that he jumped into the foundation's promotion because it dovetails nicely on Marin's healthy-is-better formula. Still, a trip to New York City couldn't hurt.

"By all means, plug that sucker on Instagram," he said with a laugh.

Fries: None, and, please; this is cholesterol-fixated Marin, remember? Instead, the burger is served with a salad. Don't be put off by the menu's populist use of the words "side salad," which is frequently synonymous with "throwaway." Not at Marin, where it's all about a well-dressed toss of noticeably fresh greens.

Take a seat: Despite its decided lack of curb appeal – it's all but invisible from the sidewalk -- the restaurant's spacious patio is one of downtown's most appealing open-air dining venues. On a picture-perfect afternoon earlier this week, I was surprised that more noon-hour diners haven't discovered Marin's urbane courtyard getaway. Think of it this way: Go for the mushroom burger, stay for the off-the-beaten-path fresh air and sunshine.

Address book: 901 Hennepin Av. S. (in the Le Meridien Chambers Hotel), Mpls., 612-252-7000. Open 6:30 a.m. to 11 p.m. Sunday through Thursday, 6:30 a.m. to 1 a.m. Friday and Saturday.