To make the crust, add flour, salt and sugar to a food processor and pulse a few times to combine. 

Add the cubed butter to the food processor and pulse a few times until coarse crumbs form.

With the motor running, pour iced water and pulse a few times until the dough just forms into large clumps. 

Turn out the dough onto a floured surface and gently knead until it comes together.

Flatten the dough into disk. 

Wrap disc with plastic wrap and refrigerate for at least 2 hours. 

Add the blueberries, sugar, flour, lemon zest and cornstarch to a bowl and stir to combine. 

Set aside. 

Preheat oven to 375ºF.

Lightly grease a muffin pan. 

On a lightly-floured surface, roll out disk until it is 1/4 inch-thick.

Use a 4-inch biscuit cutter to cut out circles of dough. 

Re-roll any scraps to make more circles. 

Press each circle into a muffin tin.

Divide the blueberry filling between the pies.

Dot the blueberries with butter. 

On a lightly-floured surface, roll out the remanning dough until it is 1/8 inch-thick.

Use a star cookie cutter to cut out stars of dough. 

Press the stars on top of the pies.

Brush the stars with beaten egg. 

Bake in preheated oven for 30-35 minutes or until golden.