Preheat oven to 425°F. Toss together raspberries, sugar, lemon juice, tapioca, and lemon zest in a large mixing bowl. Toss gently so that you don’t smash the delicate raspberries.
Mound raspberry filling into prepared bottom pie crust.
Dab pieces of butter across the top of the filled pie.
Roll out the top pie crust and place it over the top of the pie.
Tuck the top layer of crust under the edge of the bottom layer of crust, trimming excess dough. Pinch or seal the edges together.
Slit the top of the crust to allow the steam to escape while baking.
Whisk together the egg white and water. Use a pastry brush to gently brush over the pie crust.
Bake for 15 minutes at 425°F. Then reduce heat to 375°F and cover the pie with aluminum foil.
Continue cooking 25 to 30 minutes longer until the filling is bubbling up through the slits in the top crust.
Cool pie completely before slicing.
Serve with vanilla ice cream or whipped cream.