Triple Berry Slab Pie with Ginger-Lemon Streusel

Step 1

Line rimmed baking sheet with parchment paper. Roll each dough square into 16 by 11-inch rectangle on floured counter; stack on prepared sheet, separated by second sheet of parchment. Cover loosely with plastic wrap and refrigerate until dough is firm but still pliable, about 10 minutes.

Step 2

Using parchment as sling, transfer chilled dough rectangles to counter; discard parchment. Wipe sheet clean with paper towels and spray with vegetable oil spray. Starting at short side of 1 dough rectangle, loosely roll around rolling pin, then gently unroll over half of long side of prepared sheet, leaving about 2 inches of dough overhanging 3 edges. Repeat with second dough rectangle, unrolling it over empty side of sheet and overlapping first dough piece by ½ inch.

Step 3

Ease dough into sheet by gently lifting edges of dough with your hand while pressing into sheet bottom with your other hand. Brush overlapping edge of dough rectangles with water and press to seal. Trim overhang to ½ inch beyond edge of sheet. Tuck overhang under itself; folded edge should rest on edge of sheet. Crimp dough evenly around edge of sheet. Cover loosely with plastic and refrigerate until firm, about 30 minutes.

Step 4

FOR THE STREUSEL: Meanwhile, adjust oven racks to lower-middle and lowest positions and heat oven to 375 degrees. Combine flour, brown sugar, crystallized ginger, granulated sugar, ground ginger, lemon zest, and salt in bowl. Stir in melted butter until mixture is completely moistened; let sit for 10 minutes.

Step 5

FOR THE FILLING: Whisk sugar, tapioca, lemon zest, and salt together in large bowl. Add blackberries, blueberries, and raspberries and gently toss to combine. Spread berry mixture evenly over chilled dough-lined sheet. Sprinkle streusel evenly over fruit, breaking apart any large chunks. Place large sheet of aluminum foil directly on lower rack (to catch any bubbling juices). Place pie on upper rack and bake until crust and streusel are deep golden brown and juices are bubbling, 45 minutes to 1 hour, rotating sheet halfway through baking. Let pie cool on wire rack until filling has set, about 2 hours. Serve.