Andy Bell, the company's CEO, said Boomf's launch in 2013 had been "in excess of our wildest expectations", with interest from both individual consumers and large corporations.
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"Time and time again, it's hilarious to be sent pictures on your friends on marshmallows… that reaction is what works really well for us," he said. "And secondly, the other thing that's surprised us is great take-up in business settings; people using them for PR events, sending invitations or to serve at launches."
In terms of profitability, Bell said the plan was to invest in future growth at the moment, with the aim of making a profit within two years. Boomf has plans to expand later this year into the U.S., and is not limiting itself to marshmallows.
"There are more products coming out later on this year," Middleton said. "We're looking at anything from biscuits to fairy cakes, to macaroons and chocolate. But I think marshmallows are, I think, the most fun."
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Boomf is not Middleton's first foray into the world of sweet treats. He is also behind U.K.-based companies Cake Kit and Nice Cakes, although he conceded that progress at these businesses was "going slower".
He was keen to stress, however, that his royal connection was not giving Boomf a boost.
"I'm my own person, irrespective of who my family are. And I want to know I can achieve stuff without additional attention that I may get," he added.