Meghan laughed as Harry repeatedly tried to remove the sweet glaze from his fingers, as they both held piping bags.
The duchess, who shared cooking tips on her Netflix show With Love, Meghan, took on the icing task in a neat fashion, while Harry adopted a more haphazard approach.
The Duke of Sussex watches as the Duchess of Sussex arranges birthday cupcakes during a visit to Epic Partners in Nottingham (Joe Giddens/PA)
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The pair were visiting youth charity Epic Partners during their away day in the city, where they carried out their first joint public engagements since moving back to the UK.
Harry looked on as Meghan started arranging the cakes and iced letters that spelled out happy birthday, in celebration of chief operating officer Michaela Castillo-Williams, who turned 30 on Thursday.
The Sussexes sang Happy Birthday and encouraged her to take a bite out of one of the freshly-iced cakes.
Harry licks icing from his hand during the visit to Epic Partners (Joe Giddens/PA)
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The duke insisted he was the chef in the family, declaring: “That’s me.”
Epic Partners supports children, young people and families in St Ann’s and Sneinton, Nottingham, through youth work, sport, mentoring and education.
Its work combines early intervention with targeted support for youngsters affected by trauma, exclusion and exploitation.
The Sussexes were challenged to a six-ball pool game, and while Meghan politely declined, Harry accepted.
Harry and Meghan returned to live in the UK in August (Joe Giddens/PA)
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They cheered on service user Cohen, who pocketed the white with one ball left, leaving Harry to complete the match.
Meghan clapped, jumped up and down and raised both her hands up to celebrate when Harry potted his final ball, adding: “That’s so good. I’m so glad it wasn’t me.”
She then gave the duke a squeeze on the arm.
Meghan also signed an autograph for 12-year-old Kelsey, writing: “Keep shining! All my best, Meg.” – with Harry also adding his name.
Harry playing pool (Joe Giddens/PA)
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The duke and duchess also posed together with two youngsters for a selfie.
The Sussexes, who are waiting to find out whether they will be granted taxpayer-funded police protection, used their private security team for the visit to Nottingham.
But as they arrived at Epic Partners, a community protection officer could be seen walking in the area.
Five uniformed police officers also later stood guard among the crowd in the road outside, waiting for the Sussexes’ departure.
Harry and Meghan pose for a selfie at Epic Partners (Joe Giddens/PA)
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As Harry and Meghan emerged, the officers told people blocking the road to step back.
Some people held up signs saying “Please can we take a photo with you?” and “We love you”, but the couple did not stop, saying they were on a “tight schedule”, with Harry waving as he got into his Range Rover.