Eco-entrepreneur Joost Bakker has revamped his former Silo space in the CBD into Brothl, his cheekily named latest sustainability venture, via, you guessed it, broth. The idea, says Bakker, is a completely "zero waste" restaurant, using ingredients that others discard to create "rich, nutrient-dense food".

The simple menu is comprised of four broth bases: a chicken stock simmered for 24 hours, a 12-hour seafood broth, a vegetable stock made with "heaps of foraged kelp" and a 48-hour beef stock – all of which are prepared from bones and offal saved from some of the city's top restaurants.

"Most of our stuff comes from Rockpool, with Attica and Pei Modern also giving us incredible discards like fish heads, frames and marron from Attica which makes the most incredible broth," Bakker says.

The broths, and the housemade sourdough bread, are made with rainwater collected in an underground tank.

"It's particularly important for our ferments like breads and kimchi. The chlorine in tap water fights against the bacteria we actually need to grow. Also rain water is pure and the most traditional way to make broths," Bakker says.

"We also only use grass-fed frames from both chickens and beef, because we believe grain-fed animals compromise the quality and stop us absorbing the calcium through a lack of Vitamin K2 that animals only get from grass. The bones of animals and skins and cores of fruit are incredibly dense with nutrients and by using the methods we use, we are able to extract them and make the nutrients easy for the body to absorb."

Each broth costs a tenner, and diners can then add different accompaniments to each, including house-made noodles, beef brisket, chicken, kale, kim chi, bacon, soft or hard eggs and mussels (ranging from $1- $8). The serves are enormous; they're served in flowerpots, no less.

The entire menu is available from 10am, but there's also a specific "breakfast broth" (essentially a porridge, available til 2pm) for $12, made from fruit skins, seeds and even cores, which are simmered for six to eight hours, before rolled, raw biodynamic oats are added to the broth and soaked overnight.

"The oats are then cooked like porridge and served with fresh fruit in summer and poached fruit in winter, topped with crushed nuts. We also offer the oats in broth cold and uncooked," says Bakker. "It's very popular."

This 200-year-old recipe is inspired by raw-food pioneer and muesli inventor Maximilian Oskar Bircher-Benner,  but its creamy deliciousness belies its hardcore healthiness.

"It was used in his clinic to heal people who were suffering from their new diet of white breads, meat and few vegetables and fruit,"  Bakker says. "I can't believe this problem still exists today."

The cafe space itself is, of course, stylishly fitted out, with upcycled seats outside, but Brothl is not really your hungover, lingering-over-brekkie kind of spot. That said, its hearty broths are rich, filling and conscience-clearing. And, it seems, a world-first: "I don't know of any other restaurants other than our sister restaurant that's just opened in Brighton, UK, called Silo as well,"  Bakker says.

Brothl might also be just what the doctor orders. "We get a lot of people in through recommendations from naturopaths and Chinese doctors," he says. "This I love, many people are starting to understand how primitive and nourishing this food really is."