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1
To make crust:
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Preheat oven to 350F.
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Coat an 8-by-12-inch baking dish with nonstick cooking spray.
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Whisk together 113 cups whole-wheat pastry flour, baking powder, baking soda and salt in a large bowl.
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5
Beat together brown sugar, butter, oil, egg and vanilla in another large bowl with an electric mixer on high speed until smooth, making sure no lumps of brown sugar remain, about 1 minute.
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Add the dry ingredients and stir with a wooden spoon until well blended.
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(The dough will be quite firm.)
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Transfer two-thirds of the dough to the prepared baking dish; cover the dough with a piece of plastic wrap and use it to press the dough into the bottom of the dish in an even layer.
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Remove the plastic wrap.
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Bake until puffed and golden, about 15 minutes.
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To make the topping:
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Gradually work enough of the remaining 3 tablespoons whole-wheat pastry flour into the remaining dough using your fingertips, until it resembles coarse crumbs.
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13
To make filling:
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Stir together sugar, all-purpose flour and lemon zest in a small bowl.
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Combine blueberries and lemon juice in a medium saucepan; cook, stirring, over medium heat until the berries begin to exude juice.
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Add the sugar mixture and stir until the filling reaches a simmer and thickens.
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Push down the higher outside edges of the baked crust with a wooden spoon; pour the hot filling over it and spread all the way to the sides of the dish.
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Sprinkle the crumb topping over the top.
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Bake until the topping is golden, 15 to 20 minutes longer.
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Transfer the baking dish to a rack and let cool, covered with a kitchen towel to soften the crumbs slightly.
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21
Cut into 15 bars.
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Dust lightly with confectioners' sugar if using.
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23
Store at room temperature in an airtight container.
