"The Queen is a chocoholic," former palace chef Darren McGrady tells PEOPLE in this week's issue. Among her favorite sweet treats? Chocolate Perfection Pie, which she has served for lunches and dinners for years – including to visiting kings and presidents.
"It's layers of chocolate mousse, a layer of cinnamon cream and a layer of meringue," says McGrady. "It is something she still eats."
As for whether she will enjoy it on her special day this year, McGrady says, "It's possible. On her birthday she'd usually have a chocolate birthday cake. She might normally be on her own or with the duke [her husband Prince Philip]. They never really celebrated the birthdays in a big way. In the past, Prince Andrew and his girls might pop around."
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McGrady also offers insight into how the Queen has maintained her trim figure all these years.
"She has four meals a day," he says. "Here's a lady who's 5'2" and never changes [her shape]. She eats small portions. If you send up a Chocolate Perfection Pie, she'll take the tiniest slice and that's it. She has discipline."
For more on the Queen, pick up this week's issue of PEOPLE
She enjoys English breakfast tea in the mornings (Twinings is her brand of choice) and at tea time she'll have that blend again or Earl Gray.
Chocolate Perfection Pie
For the crust:
1 3/4 cups all-purpose flour
1/4 cup vanilla sugar
1 stick cold unsalted butter, cut into small pieces
1 egg yolk
3-4 tbsp. heavy cream
For the filling:
1/2 tsp. ground cinnamon
1/2 cup granulated sugar
1/2 tsp. white wine vinegar
1/4 tsp. salt
For the toppings:
6 oz. chopped semi-sweet chocolate
2 egg yolks
1 cup heavy cream
1/2 tsp. ground cinnamon
2 oz. shaved white chocolate
1. Preheat oven to 350F. Lightly grease a 9-inch tart pan and place it on a baking sheet lined with parchment paper.
2. Make the pie crust: In a large bowl or in a food processor, combine the flour and salt. Cut the butter into the flour with your hands or a pastry cutter (or pulse it in the food processor) until the butter resembles fine crumbs. Add the egg yolk and 3 tbsp. heavy cream and mix to combine. If the mixture feels to dry to come together, add another tbsp. of cream.
3. On a lightly floured surface, roll out the dough to 1/3-inch thick. Transfer it to the pan, and press the dough against the bottom and sides of the pan.
4. Line the crust with parchment paper and pie weights, and par-bake until the crust begins to brown at the edges, 15 to 20 minutes. Remove the parchment and pie weights, and cool to room temperature.
5. Prepare the filling: Place a mixing bowl over a pot of boiling water. Add the eggs, cinnamon, sugar, vinegar and salt, and whisk until the mixture starts to foam up slightly, about 3 minutes. Remove from heat and continue whisking until the mixture becomes creamy, and forms ribbons in the batter, about 3 more minutes. Pour the egg mixture over the cooled crust, and bake in the oven until the filling has risen and is firm to the touch, about 15 minutes. Transfer to a cooling rack and allow the filling to sink back into the shell.
6. Make the topping: Heat the semi-sweet chocolate in the microwave until just melted. Slowly add the egg yolks and 1/2 cup water, and whisk until combined. Spoon half of the chocolate mixture over the pie filling, and bake pie in the oven for 5 more minutes. Transfer pie to a cooling rack allow to cool completely.
7. In a large bowl, beat the heavy cream and cinnamon until stiff peaks form. Spread half of the whipped cream over the chocolate layer.
8. Fold the remaining whipped cream into the remaining chocolate mixture and spread on top of the whipped cream. Sprinkle generously with grated white chocolate and refrigerate until set, about 1 hour. Remove from pan, slice and serve.