You can't simply add brewed tea to the custard or it won't firm up properly in the oven. Instead, before you mix all the custard ingredients together, you heat the milk, stir in some Earl Grey tea ...

Pour over the hot milk and whisk. Return to the pan and whisk on a medium heat until thick. Pour into a clean bowl and cover the surface of the custard with cling. Cool and then chill. To assemble ...