Snakes have mandibles, or lower jawbones, that remain unfused, allowing them to open their mouth wider than their bodies. 

Known as gaping, this is a skill anyone facing a Mama's Boy chicken and gravy sandwich must surely pine for. For, served on the softest of white bread, with hot chicken pieces carved from an in-house rotisserie, ladled liberally with gravy and resting on a bed of shredded iceberg, it is a glory that should go in whole.

But decorum says otherwise. Mama's Boy, a tiny sandwich saloon offering well-honed filled-bread options, along with pastries, coffee, beer and fancy fizzy drinks from morning to afternoon, is a handsome spot perched in the chic and rolling streets of Surry Hills.

Co-owned by Russell Beard, also behind Reuben Hills and Paramount Coffee Project, and chef Mat Lindsay, of Poly and Ester, it used to be Shwarmama, Beard and Lindsay's kebab shop with Mark Dundon and Jin Ng. Its menu of falafel-filled pita, luxuriant hummus plates and flatbread crammed with spiced juicy lamb and marinated chicken fed the crowds from morning into the night.

Mama's Boy, which opened in November, is focusing on sandwiches and daytime hours only and, unlike Shwarmama, also features a bells-and-whistles coffee machine, AP Bakery baked goods and, in Beard's words, a warmer, more colourful interior.

"Shwarmama was sort of like a concrete swimming pool with marble benchtops," he says. "We wanted Mama's Boy to have a bit more life, colour and the feel of an Aussie milk bar."

That nostalgia begins with bright exterior hoardings advertising sandwiches called the Frankenstein, the Green Goblin, Patty Melt and, the most popular, hot chicken and gravy rolls.

The menu, hung inside and out to allow window service, features four breakfast and seven lunch dishes, the latter served from 11am. On Saturdays the breakfast line-up, which ranges from omelette and Gruyere toasties to ham, Gruyere and pickles on soft white rolls and the Green Day, a bagel filled with avocado, egg salad and pistachio pesto, is served all day.

On this Christmas Eve Saturday morning, the summer heat is rising and locals in shorts and sunnies order bulging breakfast toasties and mugs of coffee to eat at footpath tables lining the street. 

Inside, the best, and only, spot to sit is a curving window counter bar offering views of passersby, wrought iron-fronted terrace houses and tall flowering wattle trees.

An order for an egg and cheese toastie brings a carefully packed crisp-edged sandwich filled with a perfectly square wedge of sunny yellow omelette laced with Gruyere, hot zhug sauce and kicky pickles. 

Equally well-stacked is the Frankenstein, a handsomely gargantuan ensemble of whipped feta, iceberg lettuce, pickled beetroot, onion, carrot and sprouts on thick sourdough. It is a vegetarian bounty so beautifully arranged it looks like a Rothko colour field painting. 

Strong coffee comes in a curvy custom mug saying "Mama's got this" on the side and, as a mother, I am bound to agree, particularly when a rich and fragrant AP Bakery cardamon morning bun is served alongside.

Mama's Boy's pastries and bread all come from AP Bakery, another Beard and Lindsay co-collaboration, which means English muffins may hold your egg, and cheese or the Green Goblin's avocado, pistachio pesto, pickled zucchini, cucumber, sprouts and zhug is not on a bagel. 

It's also why AP Bakery's cardamon morning buns loll on the front counter alongside sticky macadamia croissants and majestic chocolate, hazelnut and toasted buckwheat twice bakes.

If you fancy a cold drink, there are Strangelove sodas, Heaps Normal non-alcoholic beer, iced lattes and long blacks and a small range of alcohol including Ok! Margarita Seltzer and Yulli's mandarin IPA and Seabass Mediterranean Lager.

"Some people will be upset we closed Shwarmama," Beard says. "But we still have chicken on a spit and it's now in a roll with gravy. That seems to be the gateway drug to bring people into Mama's Boy."

That and the ability to mimic a snake's unfused jaw and swallow it in one.

The low-down

Vibe Tiny sandwich saloon offering hot chicken and gravy rolls, vegetarian combos and egg and cheese toasties and ham, zhug, pickles, hash brown add-ons.

Go-to dish Egg and Gruyere toastie and a mug of coffee at the window counter.

Average cost for two $60, plus drinks