For the blueberry crust: Heat the oven to 350 degrees F. Butter a 9x12-inch baking dish.
In the bowl of a food processor, combine the flour, confectioners' sugar, blueberry powder, lemon zest, salt and cold butter cubes. Pulse several times until a ball starts to form. Place the dough in the buttered dish and press down firmly to form and even bottom crust. Bake until the crust is golden brown, 20 to 25 minutes. Let cool slightly. Set aside.
For the lemon filling: In a mixing bowl, whisk together the eggs, sugar, lemon juice and lemon zest. Sift the flour and baking powder together and add to the eggs. Mix well. Pour the lemon filling over the crust. Scatter the fresh blueberries over the filling. Return to the oven and bake until the filling is set when the pan is jiggled, 20 to 25 minutes. Remove from the oven and let cool completely before cutting into squares.
Dust with confectioners' sugar. The bars will keep for 4 to 5 days in the refrigerator. Try freezing the bars with wooden popsicle sticks inserted in them for a cooling summertime treat!
Assorted dehydrated fruits and veggies can be found online or at Trader Joe's, Fresh Market or Whole Foods Market.