Heat milk over medium heat in a medium saucepan until steam forms, 2 to 3 minutes. Remove from heat and add Earl Grey tea bags; steep 5 minutes.

Remove tea bags and whisk in sugar, cornstarch, and salt. Cook over medium heat until mixture is thick and bubbly, 5 to 7 minutes. Reduce heat to low and cook for 2 minutes. Remove from heat and let cool slightly.

Place egg yolks into a bowl. Pour 2 cups hot tea mixture into yolks, whisking constantly. Pour egg mixture into the saucepan and bring to a boil over medium-low heat. Cook, stirring constantly, for 2 minutes. Remove from heat; pour through a strainer into a clean bowl. Stir in butter and vanilla extract.

Pour mixture into the prepared pie crust. Chill in the refrigerator for 2 hours.

Beat heavy cream in a mixing bowl using an electric mixer until stiff peaks form, 3 to 4 minutes. Top chilled pie with whipped cream.

Return pie to the refrigerator to chill for 2 hours, or until set.