4 cups sliced rhubarb (8 to 12 stalks)
31/2 cups hulled and quartered strawberries (about 500 g)
11/4 cups granulated sugar
1/3 cup minute tapioca
zest of 1 orange
1 double-crust pie pastry; prepared and divided into 2 discs
1 egg, lightly beaten, or 1 tbsp milk
granulated sugar for sprinkling
Combine rhubarb and strawberries in a large bowl. When you’re ready to roll out pastry and assemble pie, stir sugar, tapioca and zest into fruit. Let stand, stirring occasionally, for 15 min, so that berries and rhubarb release juices.
Place rack in lowest position in oven. Preheat oven to 425F. Using a floured rolling pin, roll one disc of pastry on a floured surface into a 12-in. circle. Loosely roll up around rolling pin. Unroll over 9-in. deep-dish pie plate. Press dough over bottom and sides of pie plate. Don’t prick. Trim pastry, leaving a 1/4-in. overhang. Roll out remaining pastry disc into an 11-in. circle.
Spread filling evenly into pie crust. Moisten edge of bottom crust with water. Roll top crust around rolling pin, then unroll over filling. Trim edges, leaving 1-in. overhang.
Fold top edge under bottom edge. Crimp edges together using your index finger and thumb. Or press around edges using the tines of a fork.
Lightly brush top crust with egg. Cut small slits or a round hole in top crust for steam to escape. Sprinkle with sugar. Place pie on a baking sheet.
Bake on bottom rack for 15 min. Reduce temperature to 350F. Continue baking until bottom and top crusts are golden and fruit is bubbling, 45 to 60 min. Cool completely on a rack, at least 2 hours, before slicing. Cut into wedges.