Stir the blueberries, 3/4 cup sugar, cornstarch, water and lemon zest in a 1-quart saucepan. Cook and stir over medium heat until the mixture boils and thickens. Remove the saucepan from the heat. Cover and refrigerate until serving time.

Beat the egg in a medium bowl.

Stir 1/3 cup sugar and flour in a 1-quart saucepan. Add the milk and stir until the mixture is smooth. Cook and stir over medium heat until the mixture boils and thickens. Remove the saucepan from the heat. Gradually stir half the milk mixture into the egg. Return the egg mixture to the saucepan. Cook and stir over medium heat for 1 minute. Remove the saucepan from the heat. Stir in the butter and vanilla extract. Place plastic wrap directly onto the surface of the pastry cream and refrigerate for 45 minutes.

Spoon 1 tablespoon blueberry mixture into each pastry shell. Top with 1 tablespoon pastry cream. Repeat the layers. Top with the remaining blueberry mixture and pastry cream. Garnish with the whipped cream.