Prepare the custard by heating the milk in a saucepan over medium heat. Whisk together the yolks, sugar, and cornstarch in a bowl until combined. When the milk just comes to a simmer, stream the hot milk into the yolks while whisking to prevent the yolks form cooking. Return the mixture back to the saucepan over medium heat. Whisk the mixture until it starts to bubble. Strain the mixture into a bowl to remove any lumps. Cover the cream with plastic wrap and chill completely.
To prepare the mince, heat a pan over medium high heat with the oil. Once hot, add the shallots and cook until soft. Add the beef and break the meat up into small pieces. Season with salt and pepper. Finally add the green peas and cook just until heated through. Take it off the heat to cool.
Rachel says all the layers she arranged her trifle in. She starts with a base layer of ladyfingers, jam, custard, raspberries, then more ladyfingers, beef, more custard, sliced bananas, and whipped cream.