1Wash the berries and pat dry. Mash up 1/2 of the blueberries and put in small bowl.
In medium bown, which sugar, salt and tapioca flour. Add mashed blueberries, orange juice and orange zest and stir to combine. Let sit for 15 minute then fold in whole berries.
2Line a 9" pie plate with aluminum foil. Place blueberry mixture into foil and place in freezer until sold (about 6 hours). Once frozen, remove from aluminum foil and wrap in plastic wrap.
3Preheat oven to 325 degrees. Take one of the pie shells and place in 9" pie plate and prick bottom with fork. Remove frozen pie filling from freezer and place in prepared dough in pie pan. Place other prepared pie shell on top of the frozen fruit and seal edges. Make 2 small slips on top of pie shell. Lightly brush pie crust with egg yolk.
4Place on bottom rack of oven and bake for approx 1 hr 15 min. Allow to cool to room temperature before serving.