Back when he was the driving force behind only two budding hospitality concepts, Capitol Hill restaurateur Spike Mendelsohn looked around his slice of Southeast D.C. and figured the place could use some razzle-dazzle.

His solution: share a taste of his youth by transporting locals to a Parisian-style steak frites joint.

Voila, Béarnaise (315 Pennsylvania Ave. SE) — a paean to prix-fixe dining replete with continental touchstones such as seared foie gras, pan-fried frog legs and garlicky escargots.

Nine months later, Béarnaise is still gradually, but most assuredly, growing into its own.

There’s been no major shake-up among the leadership; Mendelsohn and veteran toque Brad Race remain firmly in control of the kitchen, while Mendelsohn’s sister and business partner, Micheline, tends to the crew at the front of the house. Custom cocktails keep materializing — there are now eight signature pours, up from the half-dozen that greeted guests on opening day — and the discount wines flow (well-curated $10 by-the-glass and value — $40 per bottle — selections), all of which makes unwinding after work with a relaxing drink affordable for nearly every budget.

Change, however, has swept across the main menu. And just about everyone seems pleased by the recent developments.

Bigger Is (Mostly) Better

According to Mendelsohn aide Jordyn Lazar, widening the scope beyond steak frites was all about keeping up with consumer demand.

“When the restaurant first opened, they featured specials like duck confit, chicken paillard and chicken liver pate. Since we’re a neighborhood spot, customers were coming in frequently and asking for those items over and over again,” Lazar said of the now-standard favorites.

Although the prix-fixe section has its admirers, other key performers — including the aforementioned paillard, a generously proportioned pork chop and well-dressed “brasserie” burger — have been promoted to featured players. Meanwhile, former anchors (farewell, locally sourced oysters) have been shelved in favor of more exotic tastes (bonjour, globe-spanning moules).

The steamed mussels, in particular, have made quite a splash.

The quartet of mouthwatering renditions (think: herby marinere, zesty Provencal, boozy Dijon and citrus-spiked curry) pulls double duty as shareable starters or self-indulgent mains.

A bowl enveloped by the scent of vermouth revealed plump specimens inundated with whole-grain-mustard-spiked cream sauce and festooned with ho-hum fried onion straws. The over-breaded vegetable was no match for the surprise waiting below — bits of lusty bacon that punctuated the surrounding liquid with peppery goodness.

Lazar said both Mendelsohn and Race are particularly fond of their duck confit plate. The meticulously crafted dish — each section of duck is cured for 24 hours in green salt and then cooked at 200 degrees for 12 hours — has quickly developed a cult following; Lazar estimates the restaurant serves up to 100 duck legs per week. The slow-and-low treatment yields a leg sporting a terrifically crispy crust shielding rich, luxurious meat. The companion spuds are hot, crunchy and hard to stop munching on (dotted with sea salt and fresh tarragon).

That goes double-triple infinity for the bone marrow.

“Wow. I was expecting, like, just a little nugget,” one awestruck companion muttered after being presented with a foot-long cavity brimming with golden, herb-sprinkled marrow. The stunningly rich spread scoops like pudding, clinging to utensils and crusty slices of butter-brushed, grilled country bread with gusto. The exposed core sports a pale yellow hue that belies its innate richness. But folding spoonfuls of caramelized onions into the equation makes each glorious bite that much more seductive.

To wit, the same friend texted a few days after we’d greedily devoured the decadent dish. “Went back to Béarnaise last night. Insisted on marrow,” she shared. “Husbands and dogs had a fulfilling evening.”

In terms of meat, playing it conservative tends to pay higher dividends.

Steak maison, an 8-ounce hunk of cooked-to-order flat iron beef, was a crowd pleaser time and time again. The well-butchered cut is attractively seared, slices effortlessly and delivers a righteous chew. Each bite of sanguine flesh was a stand-alone winner, though several house-made sauces — the cracked-peppercorn-powered au poivre and shallot-scented Bordelaise were personal favorites — complemented the entire experience (great on the fries, too).

A hefty 14-ounce entrecote looked absolutely ravishing (charred edges, bloody center, ringed by sauteed mushrooms), but proved to be alarmingly fatty.

Drinking It All In

No mere meat and potatoes joint, the restaurant also attracts discerning drinkers.

The bar, which stocks everything from obscure Gallic treasures (Armagnac, Aperol, Pernod) to cocktail staples (Bowman’s vodka, DeKuyper creme de menthe, Campari), hangs its hat on a handful of spirited tension relievers.

Hemingway’s Arrival is poetically inspired. The spiced rum and grapefruit juice achieve perfect equilibrium; no sip is too sweet or too sour, but rather, beautifully syncopated.

The Bardot Sling is even more demure, weaving together citrus vodka with orange bitters and house-made ginger shrub. The gray-tinged cooler is easy drinking and perfectly refreshing.

Mendelsohn has remained true to his vow to field value wine pours from across the globe.

The 2010 Chateau de Parenchere Bordeaux Superieur proved versatile. The merlot-carbernet sauvignon blend displayed a little pepper and some prune on the nose before spraying ripe black fruit and medium dry tannins across the palate. “It’s definitely something you could drink without food,” one barkeep rightly suggested.

A glass of Raats Old Vine Chenin Blanc got it done another night, displaying bright citrus and just a whiff of grassiness on the nose, while coating the tongue in ripe peach and sweet melon.

Of course, part of the fun of exploring wine is uncovering the ideal snack to enjoy it with — a task Béarnaise fans have, apparently, taken to heart.

Per Lazar, a couple breezed into the bar awhile back and ordered two bottles off the carefully curated reserve list. They then got to work.

“They started off with a steak tartare and escargot before their entrees,” Lazar said of a multicourse feast that ultimately involved four refills of the signature frites. “They were drinking a lovely red — what could go better with that than fries with tarragon and sea salt!” she said.