Plum-Blackberry Streusel Pie

Directions

1. 1
   Put a foil-lined large baking sheet in lower third of oven and preheat oven to 375°F.
2. 2
   Toss plums and blackberries with 1 cup sugar, tapioca, cornstarch, zest, and 1/4 teaspoon salt in a large bowl.
3. 3
   Roll out dough into a 13-inch round on a lightly floured surface with a lightly floured rolling pin. Fit into pie plate. Trim excess dough, leaving a 1/2-inch overhang. Fold overhang under and press against rim of pie plate, then crimp decoratively. Chill while making streusel.
4. 4
   Stir together oats, flour, and remaining 1/2 cup sugar and 1/2 tsp salt. Blend in butter with your fingertips until mixture forms small clumps.
5. 5
   Mound filling in shell. Crumble streusel evenly over filling.
6. 6
   Bake pie until streusel is golden and filling is bubbling, 1 1/4 to 1 1/2 hours. Cool completely, 3 to 4 hours.