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The queen’s former chef, Darren McGrady, shared the recipe for the delicious chocolate cake.

When Queen Elizabeth travels, not just any snack will do.

The Queen’s former chef, Darren McGrady, who cooked for her for 15 years, says there’s a very specific treat her majesty just has to have—even when she’s on the road.

"Now the Chocolate Biscuit Cake is the only cake that goes back again and again and again everyday until it's all gone," McGrady told Recipes Plus. "She'll take a small slice every day until eventually there is only one tiny piece, but you have to send that up, she wants to finish the whole of that cake."

McGrady explained that the kitchen turns out a variety of cakes, which the staff is allowed to finish when the royal family has had their fill. That’s not the case with the beloved chocolate biscuit cake, however. McGrady says if a slice were missing, she would notice.

Nothing better than #princewilliam favorite chocolate biscuit cake for #NationalChocolateCakeDay #EatingRoyally

Posted by Darren McGrady, The Royal Chef on Wednesday, January 27, 2016

Seriously, she loves it so much that even when she’s traveling—say, to Windsor Castle, for example—and there was some of the cake leftover, the senior chef would follow on a train with the cake. And the queen isn’t the only royal with an obsession for the decadent confection—Prince William and Kate Middleton even served it at their wedding!

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Now that must be one delicious cake!

Want to try it at home? The recipe is available on McGrady's website, The Royal Chef.