What custard tart did Jeoffrey Palmer eat in As Time Goes By?

In the British television series "As Time Goes By," Geoffrey Palmer's character, Lionel Hardcastle, often reminisces about a custard tart made by his love interest, Jean Pargetter, played by Judi Dench. The tart is fondly referred to as "Jean's custard tart." It symbolizes their shared history and evokes nostalgia throughout the series, showcasing the deep connection between the characters.