Her little market stall has grown into marshmallow empire The Marshmallowist, the UK's first producer of gourmet marshmallows which is now stocked at luxury department stores across the country.
You can forget about the pink and white stuff, Oonagh's creations are anything but ordinary - infusing unexpected flavours such as passionfruit and ginger or the popular cannabis, grapefruit and pink peppercorn creation.
Oonagh grew up in Leeds before moving to Paris aged 18, where she spent four years training as a pâtissier and chocolatier.
Her time in the City of Light inspired her dream of creating her own bespoke marshmallows and she still has a hands-on approach in the kitchen after 10 years of success.
“Our marshmallows are completely different from the pink and white marshmallows that you might recognise from supermarkets," Oonagh told the Yorkshire Evening Post.
“They're made with fruits, organic herbs and boutique alcohol - they’re almost like a souffle texture. When you’re eating the marshmallows the flavours come out in stages.
"For example, with the blueberry gin marshmallow you get the fruity tang of the blueberry when it hits your mouth, then as you finish it the floral notes of the gin come through. It’s a very grown-up way to do a marshmallow.”
Oonagh and her sister Jenny run The Marshmallowist from their base in Farsley after moving back to Leeds around seven years ago.
They offer weekly pop-up shops from their Springfield Mills kitchen, which are currently paused for the summer holidays, and have established support from Leeds locals along with their worldwide customer base.
That support has grown during the pandemic when the demand for posted gifts suddenly rocketed.
Oonagh added: “Initially when the pandemic hit, we were uncertain whether we were allowed to sell fancy marshmallows! But at a time when people need a little gift, we wanted to be there to provide that.
“The messages and notes we were writing with the gifts were so heartbreakingly beautiful. Thankfully we were able to be there for those special moments while working in a Covid-safe environment.”
The Marshmallowist added gourmet teacakes to its offering 18 months ago, quickly landing a contract to sell them at luxury retailer Fortnum and Mason.
Flavours include honeycomb mallow with a zesty marmalade centre and special edition flavours, such as the Wimbledon teacakes flavoured with Sipsmith strawberry smash gin, fresh lacerated strawberry and vanilla.
"We were really inspired by the cutting-edge trends of the chocolatier industry," Oonagh said.
"Everything is hand-painted into chocolate moulds, then we temper the chocolate and it’s filled with handcrafted caramels or jams. They’re so beautiful.”
With contracts at Harrods and Harvey Nichols, as well as being featured in Vogue, The Times and Wallpaper magazine, The Marshmallowist's signature creations boxed in luxury packaging have received high acclaim.
Oonagh added: “It’s very humbling, our aim was to work with brands like Harrods and it's amazing to work with these established names and to know that you really do produce the best marshmallows.
"In the past few years we’ve established ourselves as the leaders in marshmallows in the confectionery industry. It’s an incredible feeling, but it’s taken a long time to get there."
Support the YEP and become a subscriber today. Enjoy unlimited access to local news and the latest on Leeds United, With a digital subscription, you see fewer ads, enjoy faster load times, and get access to exclusive newsletters and content. Click here to subscribe.