1 recipe Classic Pie Pastry for a double crust (see recipe index)
For the filling-
1 pound rhubarb, rinsed, leaves trimmed, sliced ½” thick (a generous 2½ cups)
1 pound blueberries, rinsed, stems removed (a generous 2½ cups)
1 cup granulated sugar
pinch of salt
generous pinch of freshly grated nutmeg
zest of one small orange
1 tablespoon cornstarch
¼ cup finely ground instant tapioca
2 tablespoons cold, unsalted butter, cut into small pieces
egg wash made from 1 large egg beaten with 2 teaspoons water
sanding sugar for sprinkling
On a lightly floured sheet of parchment paper, roll out one circle of pie dough and fit it into a 9” pie plate. Turn the edges of the crust under itself and crimp decoratively. Set the pie shell in the refrigerator. Roll out the second circle of pie dough on a sheet of parchment paper, into a circle approximately 12” in diameter. Cover with plastic wrap and refrigerate while you prepare the filling.
Preheat the oven to 400 degrees F.
In a large bowl, whisk together the sugar, salt, nutmeg, orange zest, cornstarch, and ground tapioca. Add the rhubarb and the blueberries, using a rubber spatula to toss the mixture. Make sure the rhubarb and the blueberries are well coated with the dry mixture.
Retrieve the bottom crust from the fridge. Place the pie plate on a parchment lined baking sheet. Pour the filling into the bottom crust. Dot with the butter pieces. Retrieve the top crust from the fridge and carefully transfer the top crust to the top of the pie. Trim the edges of the top crust, fold the top and bottom edges together, sealing them, then crimping them. Cut steam vents in the center of the top crust, then brush the top with egg wash and sprinkle generously with sanding sugar. Bake the pie on the middle rack of the oven for 20 minutes. Rotate the baking sheet from front to back, lower the oven temperature to 375 degrees F, and continue baking for
an additional 35-40 minutes, until the pie bubbles up through the steam vents and the crust is golden. (Keep an eye on the pie- cover the top of the pie with a sheet of parchment or a piece of foil if it starts to overbrown.) The pie must cool for several hours before slicing.