2 tablespoons unsalted butter, cut into 1⁄2-inch cubes and chilled;
2 tablespoons whole milk, for brushing.
Whisk together the tapioca and cornstarch, 1 cup of the sugar, and the cinnamon and salt in a large bowl. Add the ground cherries, lemon juice, and vanilla. Toss to coat and set aside for 30 minutes.
Meanwhile, position a rack in the center of the oven. Place a rimmed baking sheet on the rack and preheat the oven to 425 F. (The hot baking sheet will help brown the bottom of the pie because the pastry is not baked before it is filled.)
To make the pie shell, use a lightly floured rolling pin to roll half of the pastry into an 11-inch round on a lightly floured piece of waxed paper or parchment paper. Fit it into a 9-inch pie plate, cover with plastic wrap, and refrigerate for at least 30 minutes.
To make the pastry top, use a lightly floured rolling pin to roll the other half of the pastry into an 11-inch round on a lightly floured piece of waxed paper or parchment paper. Slide it onto a baking sheet, cover with plastic wrap, and refrigerate until needed.
Stir the fruit mixture and pour it into the pie shell. It will be very full, but the fruit cooks down considerably. Dot the fruit with the cubes of butter. Cover the filling with the pastry top. Lightly press the edges of the pastry together and trim off any excess to leave a 1⁄2-inch overhang. Fold under the edge to be even with the rim of the pie plate and crimp to seal. Cut a few slits on top to allow steam to escape. Brush the pastry with milk and sprinkle with the remaining 1 tablespoon of sugar.
Place the pie on the baking sheet and bake for 30 minutes. Reduce the oven temperature to 375°F and continue baking until the crust is browned and any escaped juices are thick and bubbling, 50 to 60 minutes more. If the edges of the crust start browning too quickly, lay a flat sheet of aluminum foil over the pie. Take the pie off the baking sheet and place on a wire rack to cool to room temperature before cutting.
What else works? You can use sour cherries in place of the ground cherries.
Ground cherry pie
Ground cherries, also known as husk tomatoes, produce tiny tomato-like fruits in papery husks on low, lanky bushes.
2 1/2 cups pitted ground cherries
1/2 cup packed brown sugar
1 tablespoon all-purpose flour
1 tablespoon water
1 (9-inch) pie shell
3 tablespoons all-purpose flour
3 tablespoons granulated sugar
2 tablespoons butter
Preheat oven to 425 degrees F.
Wash ground cherries and place in unbaked pie shell.
Mix brown sugar and 1 tablespoon flour and sprinkle over cherries.
Sprinkle water over top.
Mix together the 3 tablespoons flour and 3 tablespoons sugar.
Cut butter in until crumbly.
Top cherry mixture with crumbs.
Bake for 15 minutes. Reduce oven temperature to 375 degrees F and continue to bake for 25 minutes.