Prepare pie crust and refrigerate at least 30 minutes if not overnight.
Roll out the pie dough in a circle large enough to fit your pan.
Toss frozen blueberries with flour.
Add sugar. Add lemon juice. Mix.
Add cornstarch. Mix. This will help thicken.
Place rolled out pie dough in cast iron pan or pie pan.
Fork the dough.
Add the berries.
Cut out circles of pie dough with a biscuit cutter and place over berries.
Paint milk over the circles (helps with browning). Toss sugar over the tops.
Bake at 400 for 50-60 minutes or until golden brown.