“Mary’s” sounds like a biker bar in Missouri, but it’s actually a smart-casual brasserie from Jason Atherton close to Hanover Square, London. It was, until recently, Pollen Street Social, but it’s now a case of new name, new menu, softer edges, and more of a come-one come-all, pre-theatre, boozy-treat, long-lunch vibe. Taking a Michelin-starred restaurant and turning it “casual” is always controversial in the foodie world. Not only are you pricking the bubble of those who adore pomp and small portions, but you’re also annoying people who like telling you that they’ve experienced this pomp everywhere from Dundee to Dubai. So when the likes of Atherton suddenly tells staff they can wear jeans, begin serving steaks and doughnuts, and allow the words “Mary’s dirty burger” to enter the fray, pearls will be clutched. Or, more accurately, someone called Douglas in a cummerbund in Cirencester will insist furiously that Mary’s was better in 2012, when his meal took three hours and there were more dishes with translucent, 42-hour consommé and shards of yeast. The paper tablecloths, the soft-serve ice-cream sundaes, the offer of curry mayo on the two-course £29 prix fixe are all daggers to the heart of fancy diners. It’s important, however, to say right now that Mary’s, despite everything above, retains rather a lot of pomp. Atherton has not gone mad, opened a Wimpy and begun serving slop. Quite the opposite: this is a large, elegant, pale room with plenty of light from the vast windows looking down on to Pollen Street. The walls are festooned with modern art, the staff are still drilled to politeness (they’re diligently friendly to solo diners) and, most importantly, chef Alex Parker’s menu is still secretly fancy. Expect Lyonnaise onion agnolotti, Orkney scallops with ajo blanco, rabbit leg with lovage persillade butter, grass-fed tomahawk and Cornish brill with surf clam pil pil. I have not faced down “Mary’s dirty burger”, but closer scrutiny tells me this is good-quality Cumbrian beef stacked with deep-fried pickles and served with Koffmann’s chips and a choice of black garlic aïoli or truffle mayo; you can also eat this burger sitting on a tall stool in the adjacent Blind Pig bar. Eagle-eyed readers might say, “But Atherton’s Blind Pig is a mile away on Poland Street?” Not any longer; the Blind Pig is now part of Mary’s. Over recent months, tracking the Atherton empire’s global transmogrifications requires a large whiteboard and several pens; he’s opened about 40 restaurants over the past 20 years, and now there’s Sael on St James’s Market, the forthcoming Three Darlings in Chelsea, Hot Dogs in Harrods and Row on 5 on Savile Row. Suffice to say, diners who are irked that the former Pollen Street Social is now more user-friendly is the least of Atherton’s worries. Not least because Mary’s is hugely enjoyable: she’s kicked off her shoes and taken the pins out of her barnet. No longer a place to eat daintily, this is now a place to eat rather too much. Expect things with posh names to be battered or breaded – apologies, in tempura or panko crumb – such as top-grade monkfish or a hash of duck breast served in a puddle of rich, silky satay sauce and topped with pickled cucumber. That chunk of tempura monkfish arrives crisp, hot and slathered with warm, freshly made tartare. A side of humble-sounding bobby beans come in a rich tomato fondue with fresh parsley, and there is globe artichoke barigoule for those grasping at health; however, if you’re here on Earth for a good but not a long time, please order the Lincolnshire potato with cabbage, onion and caviar, a soft, heavenly mush of cream, cheese, chive and roe. Or, for that matter, any of the day’s grilled fish – mackerel, john dory and skate on the day I went – which is served with lashings of café de Paris butter. The pudding list is, as you’d imagine, a menace to public health. There was a very good, warm, boozy, cheek-flushing doughnut with calvados-powered custard and plentiful cinnamon sugar, and a Basque cheesecake made with orange, chocolate and tonka bean. There is a chance that by 2028 Atherton might be running all the restaurants and employing all the chefs in the western hemisphere. I would try to be more uppity about this, but I’m still too high as a kite on the calvados doughnut to take the higher ground. Mary’s, 8-10 Pollen Street, London W1, 020-7290 7600. Open Tue-Sat, lunch noon –2.30pm, dinner 5.30-11pm (6.30pm prix fixe). About £60 a head à la carte; set menu two courses for £29, three for £35; all plus drinks and service. The next episode of Grace’s Comfort Eating podcast is out on Tuesday 1 October – listen to it here