In a mixing bowl, add the dry ingredients and mix well. Chop the butter into small cubes.
In a high speed blender or food processor, add all your ingredients and blend well, until a fine and crumbly texture remains.
Form two smooth balls with the dough and cover them completely in plastic wrap. Refrigerate the dough for at least two hours.
Preheat the oven to 180C/350F. Grease a 9-inch pie dish and set aside.
In a small saucepan, add the blueberry filling into a small saucepan and place over low heat. Once it begins to simmer, gently stir it for 4-5 minutes, before removing it from the heat.
Place the two balls of dough amongst two pieces of parchment paper. Roll out the dough, allowing one of them to be larger than the other. Place the larger of the two pieces of dough into the pie pan, allowing the sides to overhang. Fill the pie with the filling and spread it out until it is mostly even. Top with the second layer of dough, and crimp the sides. Brush with the egg wash.
Place the pie in the oven and bake for 45-50 minutes, or until golden brown on top. Remove the pie from the oven and let it cool for several minutes, before serving.
Notes
TO STORE: Blueberry pie should be stored in the refrigerator, covered. The pie will keep well for up to 2 weeks.TO FREEZE: Place the pie in a shallow container and store it in the freezer for up to 6 months.