The seemingly-easy process works by linking an Instagram account with the Boomf website and picking nine favourite pictures to put on 4cm by 4cm marshmallows, all costing £12 (sounding even better).
Middleton's involvement has only recently been released in order to ensure a smooth launch for the enterprise.
Middleton, who is also the entrepreneur behind Nice Cakes, approached Mint Digital with the idea of Boomf last year as he needed help with the web build.
"A guy called Steve Finan introduced me to Mint," explains James.
"We were watching Andy Murray at Wimbledon last summer. I was telling him about my Instagram marshmallows idea and he suggested I talk to Mint. I was impressed by their previous projects: StickyGram and Projecteo.
"When I met Mint we clicked from the start. We have a very similar vision but are coming at it from totally different angles: Mint from digital and me from food. I think the most fun we had was coming up with the name: Boomf is the noise a marshmallow makes when it falls through your letterbox."
Erm. We're not sure about that, but we like the idea.
See pics of James' rather famous sister right here: