Preheat oven to 375°F and prepare a 13x9 baking dish by spraying with a non-stick spray; make sure to spray the sides and corners well.
In a mixing bowl, toss the blueberry filling together and set aside.
In a large bowl, add in flour, baking powder, salt, granulated sugar and lemon zest. Mix to combine.
Using your fingers press and combine butter into flour mixture. You may also use a pastry cutter or even a food processor, if you wish. I find it just as easy to use my hands.
Once the butter is all incorporated, mix in the egg yolk,vanilla extract and brown sugar.
Pour in lemon juice and water. Mix the dough with hands or a wooden spoon until the dough is combined yet crumbly. You should be able to press the dough together between your fingertips and it mostly stays together.
Press two-thirds of the crust mixture into the bottom of the prepared baking dish. Use your fingertips to push the mixture together as well as pushing it into the corners and along all edges of the pan.
Set aside the reserved ⅓ of the dough.
Gently, pour in the blueberry mixture on top of the dough. Use a spoon to spread it out evenly.
Sprinkle the rest of crust mixture over the top of the blueberries. It will not completely cover all the blueberries.
Bake for 40 to 45 minutes at 375°F.
Blueberry lemon bars are done when the blueberries are bubbly and the top is golden brown.
Allow the bars to cool at least 30 minutes or until completely set. Room temperature is best, but they’ll smell so good you may not be able to wait.
Sprinkle powdered sugar on top if you wish.
Serving - serve blueberry lemon crumble bars right out of the oven or heat them up in the microwave and top with a scoop of vanilla ice cream or add a dollop of chantilly cream.