Preheat at 400 F 204 C.
Mix together egg and water to make a egg wash.
Mix together in a bowl blueberries, splenda, flour, cinnamon, allspice, salt, then pour into prepared pie crust.
Drizzle lemon juice over mixture then drop butter on top of mixture.
Add top crust, cut slits in top to vent and brush with egg wash.
Bake for 45-50 minutes.
Cool at least 2 hours before serving.