In a new YouTube cooking tutorial, the chef walked royal fans through how to make banana flan, which he described as "nursery food".
The "super easy dessert" is made up of banana custard in a pastry shell, topped with chopped bananas and brushed with apricot jelly. Yum!
Darren, who worked at Buckingham Palace for 11 years followed by Kensington Palace for four, explained: "You can't send rose petal panna cotta with lavender shortbread up to a five-year-old Prince William, can you? He doesn't have that sort of palette yet."
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He continued by revealing banana flan, or banana tart, was one of the young Princes' favourite dishes – so much so that they would rush into the kitchen to see him after school!
Princess Diana's sons loved banana flan as children
"Whenever the boys were home, Princess Diana would write banana flan in the menu book. And then she'd write H or W at the top to let me know who was coming," Darren said. "The boys would come back from school on a Friday to Kensington Palace and come in the kitchen, 'What's for dinner, Darren?' They'd see the banana flan on the side and say, 'Yes!'"
So how do you make Prince William and Prince Harry's favourite dessert? Darren shared a clever cooking tip to perfect the custard for those trying the royal recipe at home – cornstarch is a huge time-saver.
Darren McGrady revealed the royal dessert is "super easy" to bake
"The great thing about using cornstarch in this is that once that liquid gets hot enough to open up the cornstarch granules, then it starts to thicken automatically. If you were using flour, you'd actually have to cook this and let all those starch granules open, which can take about 20 minutes to lose that floury taste," he revealed during the video.
For the finishing touches, Darren suggested layering the bananas on the top of the tart starting from the outside, overlapping as you go. Once you've created the pretty layered design, the royal chef added the glaze – which is as practical as it is delicious.
"The glaze is to give it some sweetness but also to protect those bananas so they don't go all brown and nasty," he said.