1. It is best to start with making your filling because it has to be cooled to room temperature before being used to fill the pie.

For the Blueberry Filling

1. Whisk together the flour, sugar, brown sugar, cinnamon and nutmeg.
2. In a large saucepan, bring the blueberries, lemon zest and lemon juice to a gentle boil.
3. Stirring constantly, gently stir in the flour, sugar and spice mixture. Cook for only a minute after the last of the dry mixture has been stirred in. Your filling should now have thickened.
4. Remove from heat and stir in the 3 tbsp butter.
5. Cool the filling to room temperature before adding to the pie crust. This is very important or your bottom pie crust will be soggy.
6. Pour into prepared pie crust. Top with the second pastry round, tucking the edges of the dough under the bottom crust and flute the edges together using your fingers or a fork. Brush with egg wash made by whisking together 1 large egg yolk & 1 to 2 tbsp water
7. Lightly sprinkle sugar over the top of the egg washed pie if you like. Turbinado sugar works well for this. Slit a 1 inch hole in the middle of the top crust to allow steam to escape.
8. If you prefer to make a lattice crust on top, roll the second dough round into a 12 inch square-ish shape and cut that into 8 equal strips for the lattice crust top. Place the pastry strips on top of the blueberry mixture, interweaving them to form a simple lattice pattern. Tuck the ends of the strips under the edge of the bottom crust and crimp with a fork or your fingers to seal the pastry together. Brush the edges of the crust and the lattice top with an egg wash.
9. Chill the pie in the fridge for 20-30 minutes. This will help make a flaky crust. Place the pie on a cookie sheet to catch any dripping filling as it bakes. Bake at 400 degrees F for about 20 minutes, then reduce heat to 350 degrees F or until filling bubbles and thickens, about 45 minutes to an hour. If the crust begins to get too dark around the sides, cover the edges with strips of aluminum foil and continue baking until the rest of the pie is completely baked. Cool completely before serving.

To prepare the pastry

1. Using a food processor or a pastry blender cut cold shortening and butter into flour, brown sugar and salt until mixture resembles a coarse meal. Small pieces of shortening and butter should still be visible.
2. Pour vanilla into cold water then pour over the mixture and work in by tossing with a fork until dough begins to form. Use your hands as little as possible and work the dough as little as possible.
3. Divide dough into 2 balls, flatten into 2 rounds, wrap in plastic wrap and place in the refrigerator to rest for a minimum of 20 - 30 minutes.You can make your dough the previous day but make sure you take it out of the fridge for 10 minutes to warm slightly before rolling out.
4. Roll the dough into a 12 inch round and place in the bottom of a 10 inch pie plate. Push the dough well into the pan to make sure that it is not stretched at all. This is important to make sure your dough does not contract during the baking time. Trim the dough to edge of plate by running a sharp knife around the edge.
5. Roll the remaining dough round into a 12 inch round and reserve for the top of the pie.