The burger: When Mattie’s on Main opened last year, my polite response — to the food, anyway — could have been filed under “underwhelmed.”

That’s changed. Co-owners Dean Schlaak and Tom DeGree — they’re the couple behind neighboring Wilde Roast Cafe — have rebooted their Riverplace restaurant, bar and music venue, starting with a smart new hire in the kitchen: chef Nathan Docken.

In just a few short weeks, Docken, a Coup d’etat vet, has completely reinvented the Mattie’s experience. His strategy is uncomplicated, and seemingly foolproof: Concentrate on seasonal, locally sourced ingredients, and treat them with respect. It also helps that he knows what he’s doing.

Docken’s initial success at Mattie’s is encapsulated in a fiercely delicious burger. Docken wisely keeps it simple, focusing his energies on selecting the just-right components and then showcasing them to their best advantage. The lean, grass-fed ground beef (sourced from Grass Run Farms, a collection of family-owned, quality-fixated Midwestern farms) exudes plenty of clean, beefy flavor, a quality enhanced only by salt, pepper and the heat of the flattop grill. Docken shapes it into thick, loosely formed and roughly hewn patties, laying it on in what feels like third-pound increments and cooking them precisely to order, leaving a lightly crusty char on the outside and a juicy, delicately pink interior.

Finishing touches are kept to a minimum, all while staying safely within the borders of Unbeatable Combination, if such a nation exists. Smoke-laced bacon, hailing from premium Niman Ranch, is cut thick, nurtured on the stove to maximum crispiness and then criss-cross-ed over the top of the patty, the strips hanging out beyond the bun's edges, a visceral symbol of ork-ified excess at its best.

Cheese is a punchy five-year-old Cheddar from Hook’s Cheese Co. in Mineral Point, Wis., truly one of the great exports from our dairy-obsessed neighbor to the east. Direct from the garden — because that’s how delicately fresh it tastes — is a blanket of a lettuce leaf. A few raw red onions add a welcome spark.

The soft, milky, lightly toasted bun (a Franklin Street Bakery product) is right on the money, although it might be a tad too big for the patty; the bread/beef ratio feels slightly off. But when the total package is this good, it seems silly to complain.  

Docken isn’t content with a single burger entry. Another invokes the same beef patty (and terrific, if slightly plus-size bun), but tops it with a just-right over easy egg (the white nicely browned, but the yolk still runny), a prodigious amount of creamy Gruyere, a sprinkle of tangy pickled onions and a side of zesty sambal-flavored aioli, a sweet-and-spicy condiment Docken also serves with his cheese curds.

It’s $14 (pictured, above). A second ($16) calls upon ground elk.

“I like that it isn’t overpowering like other game animals,” said Docken. “Its gamey texture is more subtle, it doesn’t overpower you.” He tops it with tangy goat cheese from Stickney Hill Dairy in Kimball, Minn. (“I’m in love with that chevre,” he said) and bits of pork belly scrap — a leftover from Sunday brunch — that he fries off as bacon bits. Next time I hit the movies at St. Anthony Main, that exercise in elk is going to be my pre-film dinner.

So far, so good, right? “I’m having a lot of fun,” said Docken. It shows.

Price: $13.

Fries: Included, and recommended. They’re skin-ons, taken to a deep golden color in the fryer and tantalizingly crispy and salty.

Tasty as they are, I’d like to make a plea for the side salad. In Burger World, the words “side salad” are usually synonymous with indifference, with the kitchen inevitably treating a handful of flavorless, straight-out-of-the-bag mixed greens as an afterthought, at best.

Not here, and that’s a credit to Docken’s no-stone-unturned work ethic. Crisp, freshly minted mesclun is tarted up with endive and bitter greens, splashed with a pert sherry vinaigrette and dressed with crunchy black walnuts, thin slices of juicy Fuji apples and a crumble of that extra-sharp five-year-old Cheddar. Yep, this well-thought-out beauty is a “side” in name only, and worth every penny of its $3 upcharge.

And now, for something completely different: Under Docken’s tutelage, Mattie’s, which has the great fortune of being located in one of the city’s most densely populated residential districts, has been wisely retooled as a neighborhood destination.

The bar menu appears unchanged. The amusing — and delicious — array of ice cream drinks remain, as does the commitment to tapping a wide range of local craft beers, 18 in all.

As for the kitchen’s output, it’s truly a night-and-day difference. Docken offers beer-friendly, drop-by-for-a-snack options, including house-baked pretzels with a beer-cheese sauce, lemony fried Brussels sprouts, cheese curds, and steamed mussels seasoned with chorizo. The aforementioned burgers are supplemented with a half-dozen other sandwiches; I’ll definitely return for a crack at the barbecue pulled chicken and the tilapia tacos with a roasted sweet corn salsa.

There are a few salads, too. Previously, I would have been shocked to encounter colorful, ripe-with-juices heirloom tomatoes at Mattie’s. No longer. Docken is getting his hands on some real beauties, slicing them into hefty wedges and pairing them with slabs of mozzarella, drizzles of basil-infused balsamic vinaigrette and twinkling flakes of sea salt; it's the essence of August in Minnesota, and a relative bargain at $9. Larger appetites can take refuge in a quartet (squab with sorrel and chanterelles, butternut squash-filled agnolotti) of serious-minded, upper-$20s entrees.  

As for dessert, Docken is offering a coconut panna cotta finished with a peach compote, a fig crostata and other late summer-appropriate delights, and they sound tempting. But to be honest, whenever I find myself in this neighborhood, I can’t help but immediately get a hankering for the fudgy, no-frills brownies and the chewy Special K bars sold at the counter at the Wilde Roast. They’re lovingly prepared, they’re big enough to share (and share, and share) and they’re portable, which makes them ideal post-burger sweets during an after-dinner summer stroll along S.E. Main Street. The downtown skyline views are seemingly plucked straight off of Instagram, and if you haven’t taken in the visual splendors of nearby Water Power Park, you need to, today.

The restaurant’s name — formally, it’s Mattie St. Clair’s House of Spirits on Main Street — is a nod to a brothel operator of the same name, who plied her trade in the neighborhood in the late 19th century. It remains something of a hodgepodge, with a four-sided (and easily bellied-up-to) bar separating a black-and-white-and-red music room and a long, narrow, full-of-potential greenhouse-style space that runs along SE. Main St.

Stepping under its curved glass roof is a total late-1980s time warp — the metalwork is awash in a particular shade of green that hasn’t seen the light of day since “Thirtysomething” left the airwaves — and Schlaak and DeGree haven’t quite made it work. More greenery, perhaps? It doesn’t help that the restaurant is located smack in the center of Riverplace, aka the Ghost of Shopping Centers Past. Diners must traverse the dreary, off-putting tomb to late-80s excess if they're entering the restaurant via the complex’s handy parking ramp (be sure to ask for a validation ticket), and the emptiness is a downer. Better to approach from lovely SE. Main Street.

Address book: 43 SE. Main St., Mpls., 612-886-2121. Kitchen open 4 to 10 p.m. Sunday through Thursday, 4 to 11 p.m. Friday and Saturday. Brunch 9 a.m. to 1 p.m. Sunday.

Talk to me: Do you have a favorite burger? Share the details at rick.nelson@startribune.com.