Before beginning, preheat your oven to 375 degrees. Line a 9x13 pan with parchment paper and spray the bottom. Make sure to leave parchment paper extended over the edges, so you can lift out the entire pan of bars once cooled. (If not using parchment paper, simply spray baking pan with non-stick spray).

Place flour, 1 CUP of the sugar, baking powder, cinnamon, salt and lemon zest into a food processor. Pulse a couple times to mix. Add egg, butter, and vanilla extract. Pulse the mixture until dough gets crumbly (and butter is size of small peas).

Put HALF of the dough mixture into the baking pan. Pat down with fingers to form a solid crust. Set aside the rest of the mixture to use for the crumb topping.

In a large mixing bowl, combine the rest of the sugar, cornstarch and lemon juice. Add the blackberries, and stir gently to fully coat berries. Spoon the blackberries over the crust in the pan. Sprinkle the remaining crumb mixture over the top of the berries.

Bake at 375 degrees for 45 minutes (or until the topping is golden brown). Remove to a wire rack. COOL COMPLETELY before lifting the bar cookies out of the pan (using the parchment paper).

Cut into serving sizes. (It is easy to cut into bars if you use a pizza cutter!) Enjoy!