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."
And you don't have to be a Windsor to eat like one. Check out the recipe for Prince William's favorite dessert below:
Banana FlanServes 6
For the pastry – enough for two tart shells:
¾ cup plus 1 tbsp. sugar
3 ½ sticks butter, in small pieces
1 tsp. vanilla
3 ¼ cups flour
For the filling:
1½ cups milk
½ cup heavy cream
5 egg yolks
¾ cup granulated sugar
2 tsp. vanilla
¼ cup cornstarch
pinch of salt
1 tbsp. unsalted butter (softened)
3-4 ripe bananas, sliced ¼-inch thick
½ cup apricot jam
1. In a food processor, combine sugar, butter, egg and vanilla. Pulse until smooth. Add the flour and pulse until combined. Turn out onto a floured surface and form into two balls. Cover each with plastic wrap and refrigerate for at least 2 hours. (Unbaked dough may be refrigerated for up to one week or frozen up to three months.)
2. Roll out one ball to about ¼-inch thick circle and place it in a 9-in., two-piece tart pan. Refrigerate for about 45 minutes. Preheat the oven to 425º. Line tart with parchment paper and fill with baking weights. Place tart in oven. After 5 minutes lower temperature to 375º. Bake for another 10 minutes. Remove parchment and weights and bake until tart is golden brown, about 10-15 minutes. Remove from oven and cool completely.
3. In a large saucepan, bring the milk and cream to the boil. In a large bowl, whisk together egg yolks, egg, vanilla, cornstarch and salt. Slowly add the hot milk and cream into the egg mixture, whisking constantly. Pour the contents of the bowl back into the saucepan. Continue whisking pastry cream over medium heat until it thickens, about 5 minutes. Remove from the heat and whisk in butter. Let cool slightly, then spoon into the tart shell.
4. Arrange banana slices neatly on top of the warm filling. In a small pan, bring the apricot jam to a boil and brush over the top of the bananas.
(Adapted from Chef Darren McGrady's Eating Royally)