Claire Ptak says Prince Harry and Meghan Markle’s culinary centrepiece will be presented in a special installation.
It has already emerged that the layered lemon and elderflower cake will consist of three parts of varying sizes.
The final design will not be unveiled until the big day but the royal couple are said to fully back the plans.
Ms Ptak said: “You’ll have to wait and see on the day. It’s an installation of the way that we’re putting it out. It’s the last thing that we’ll reveal.
“It’s a non-traditional layout. It’s a slight shift from tradition.”
She described the flavour of the cake as a balance of sweet and tart, coupled with an “ethereal” elderflower.
In at least one of the tiers, several layers of lemon sponge which have been drizzled with elderflower syrup are separated by a curd flavoured with Amalfi lemons.
The tier has then been covered in an elderflower Swiss spring buttercream.
“(It) is a buttercream that is very light and fluffy, kind of satiny,” Ms Ptak added. “Super delicious. So the texture is really lovely and the flavour is quintessentially spring and British.”
The cakemaker, whose Violet Bakery is based in east London, has been working in the kitchens at Buckingham Palace for the last five days.
The separate parts will be transported to Windsor Castle where it will be assembled in situ on Saturday morning. Then, the flowers will be added.
Californian Ms Ptak, who spent three years working for Michelin-starred influential American chef Alice Waters before coming to the UK, is thought to have met Ms Markle when the actress interviewed her for her blog.
She described the royal couple’s taste as aiming to celebrate what is freshest at the time.
She said: “They, like me, really like to enjoy to eat what’s in season and really celebrate what’s the freshest, most delicious thing at the moment in time.
“So they share that same philosophy with me and with a lot of people.”
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:: Sky News is broadcasting live from Windsor with all the build-up to the royal wedding, with exclusive live coverage of the wedding in UHD in a special programme from 9am to 3pm on Sky News and Sky One this Saturday.