INGREDIENTS
Dough for a double-crust pie, chilled (see recipe; be sure to double it)
2 1/2
cups/312 grams rhubarb, trimmed and cut into 1/2- to 1-inch lengths
1 1/2
cups/226 grams blueberries or blackberries
3/4
cup/150 grams granulated sugar, more for sprinkling
2 tbsp
all-purpose flour
2 tbsp
quick-cooking tapioca (also called instant, minute or small pearl tapioca)
1/3 tsp
salt
freshly grated nutmeg
1 tsp
fresh lemon juice
1/2 tbsp
cold unsalted butter
1
egg white, whisked with 1 tablespoon water