Preheat oven to 450 degrees F. Combine first 5 ingredients in a bowl, and then spoon into pie shell. Top with butter pieces. Brush edges of the pie with egg wash. Set on top crust and crimp the edges to seal.
Brush top with egg wash and sprinkle with sugar. Cut a small whole in the centre of the pie to allow steam to escape.
Bake pie 10 minutes. Reduce heat to 350 degrees F and bake until golden brown, about 35-40 minutes more.