For the upcoming royal wedding, Princess Diana's former chef Darren McGrady predicts guests will enjoy formal English fare. But when it comes to Prince William's favorite food, one decidedly unstuffy dessert tops the list: Banana Flan. McGrady used to serve the dish (displayed above on Diana's favorite "Herend Birds" china) during private lunches he prepared for the Princess, William and Harry in the dining room at Kensington Palace. "On these occasions, William and Harry could eat what they wanted," McGrady tells PEOPLE. "Two or even three slices of banana flan were perfectly okay as long as 'my boys' are happy – that was how the boss thought." And the dessert – akin to banana cream pie – has a Royal pedigree: "Both William and Harry loved banana flan," says McGrady. "It's the ultimate in comfort food or 'nursery food' as the Queen would call it. In fact, the Queen herself used to be served it as a child, too...