In a med-sized bowl, whisk together the flour, brown sugar, granulated sugar, cinnamon & salt until well blended. Work the butter into the flour mixture with your fingertips, until it looks sandy, with no large pieces of butter remaining. Press the mixture together to form chunks. Set aside in the refrigerator until ready to use
Preheat the oven to 350ºF (180ºC). Line an 8” square baking pan with parchment paper, leaving a couple of inches of overhang
In a med-sized bowl, whisk together the flour, powdered sugar, baking powder & salt until well blended. In a large bowl, beat the butter until smooth. Add the flour mixture & beat just until combined
Press the dough evenly into the baking pan. Bake until the surface looks light golden brown, about 20 min. Meanwhile, prepare the filling.
In a large bowl, toss the blueberries with the lemon juice. Mix in the sugar & cornstarch.
Pour the blueberry mixture over the warm crust. Top evenly with the crumb topping. Return the pan to the oven & continue baking until the topping is golden brown & the filling is bubbly, about 28-35 more min.
Let cool completely before removing the bars from the pan. Sprinkle with powdered sugar
