Preheat oven to 375℉

Sprinkle a couple tablespoons of flour onto a cutting board or counter top. Roll out one sheet of the pie crust onto the floured surface. Gently roll out with a rolling pin until smooth. Fold the pie sheet in half and place into the bottom of the pie dish. Unfold and mold into the bottom and sides of the pie dish.

Rinse blueberries and add to a mixing bowl. Sprinkle berries with lemon juice, cornstarch and sugar. Toss gently to coat the berries.
Add the berry mixture to the pie dish.

Slice chilled butter into pieces and place on top of the berries.

Unroll the second sheet of pie crust to the floured surface and roll gently to smooth. Using a pastry wheel, cut the rounded edges off of the pie crust sheet, then cut into strips as evenly as possible. Add the strips in one direction on top of the pie spaced apart. Weave in strips going the opposite direction over and under each strip for form a lattice pattern.

In a small bowl, add the egg yolk and tablespoon of heavy cream and whisk together. Use a pastry brush to brush on the top of the crust.

Place pie into the oven and bake 45-55 minutes until hot and bubbly. The crust should be nicely browned. Allow the pie to cool completely before serving.