Plum Crumble Bars

Yield: 12 bars

          nonstick cooking spray, for the pan
Filling:
1½     pounds black plums, halved and pitted
²⁄³      cup granulated sugar
          pinch kosher salt
¼       teaspoon ground allspice
¼       teaspoon ground cardamom
¼       teaspoon ground cinnamon
¼       teaspoon ground ginger
4        teaspoons arrowroot
1        teaspoon fresh lemon juice
Crust/Crumble:
2        cups unbleached, all-purpose flour
¹⁄³      cup granulated sugar
¼        cup packed light brown sugar
1         teaspoon kosher salt
½        teaspoon grated lemon zest
14      tablespoons (1¾ sticks) very cold
           unsalted butter, cut into pieces
¹⁄³      cup rolled oats
1         large egg white whisked with 1
           teaspoon water, to seal crust

Nutritional information per bar:
Calories 310 (39% from fat) • carb. 45g • pro. 3g • fat 14g • sat. fat 8g • chol. 35mg • sod. 109mg calc. 49mg • fiber 2g

1. Preheat oven to 375°F with the rack in the middle position. Lightly coat a 9 x 9-inch pan with nonstick cooking spray and line with parchment paper, leaving overhang on two sides.
2. Prepare the filling. Insert the slicing disc, set to 7mm, into the food processor. Slice the plums. In a medium bowl, whisk together sugar, salt, and spices. Add the plums and lemon juice, and gently toss with your hands until well mixed. Set aside to macerate. Clean out the work bowl.
3. Make the crumble. Insert the chopping blade into the work bowl. Add the flour, sugars, salt, and zest and process on Low for 10 seconds to sift. Add butter and pulse in 3-second long bursts until the mixture is very sandy and crumb-like, about 15 pulses. Transfer 1½ cups of the crumble into a small mixing bowl. Mix in ¹⁄³ cup oats with your hands, pinching the mixture together until crumbs form.
Cover with plastic wrap and refrigerate until ready to bake. Transfer the remaining crumble to the prepared pan and press into an even layer to form crust. Freeze until firm, about 15 to 20 minutes.
Prick all over with the tines of a fork and bake until golden brown, about 18 to 20 minutes. Remove and set pan on wire rack. Lightly brush with egg wash and let cool completely to room temperature.
4. While the crust cools, drain the plums in a strainer set over a medium saucepan. Return the slices to the bowl. Bring the juice to a simmer over medium heat. Reduce heat and continue to cook, stirring frequently, until thickened, about 3 to 4 minutes. Remove from heat. Allow to cool, then whisk in arrowroot and lemon juice.
5. Bake the bars. Mix the cooled syrup into the sliced plums. Pour the filling over the cooled crust and spread in an even layer. Sprinkle the remaining crumble evenly over the top. Bake for 50 to 55 minutes, until filling bubbles at edges and the crumb topping is golden brown. Remove from oven and set on a wire rack. Let cool completely in pan.
6. To serve, use a sharp knife to release edges. Use parchment overhang to lift the bar from pan and transfer to a cutting board. Cut into 12 rectangles.