Mix flour, sugar, salt in a bowl. Cut in cold butter. Break up butter and slowly add cold water. Wrap in plastic wrap, and place in fridge for 30 minutes.
Filling
While the crust dough is chilling, start on the filling.
In a medium-sized saucepan over low heat, add the chopped & pitted cherries, blackberries, raspberries, sugar, cornstarch, lemon juice, water, vanilla, and salt. Stir until combined.
Turn the heat up to medium-high and allow the mixture to boil.
Once boiling, turn down the heat and let the mixture simmer until it is thickened about 5 minutes.
Topping
In a small microwave-safe bowl, melt the butter.
Add the remaining ingredients: flour, brown sugar and cinnamon.
Stir until it comes together.
Assemble
Preheat the oven to 400 degrees.
Grease a 9x13 pan with non-stick spray. Remove the dough from the fridge and roll it out to fit the pan size. Press the dough into the bottom of the pan.
Pour the cooled pie filling on top of the crust.
Sprinkle the brown sugar topping on top.
Bake for 45 minutes
Remove and allow the pie bars to cool completely before slicing. This takes about 2 hours. If you slice it too early, the center will not be set.