Add the pitted cherries to a saucepan along with brown sugar, fresh lemon juice and lemon zest
Cook over medium heat until the cherries begin releasing their juices.
In a small bowl, mix corn starch with 4 tbsp water to make a smooth slurry. Pour the corn starch slurry into the cherry mixture and keep stirring continuously until the filling thickens.
Turn off the heat and let the cherry filling cool completely to room temperature.
In a large mixing bowl, combine all-purpose flour, granulated sugar, brown sugar, baking powder, and salt.
Add melted butter and vanilla extract to the flour mixture. Mix using a spatula or fork until everything is evenly combined and forms a crumbly mixture.
Preheat the oven to 350°F (175°C).
Line an 8×8 inch baking tray with parchment paper.
Transfer about ¾ of the prepared crumble mixture into the tray and press firmly to create a flat, even crust.
Spread the cooled cherry filling evenly over the crust.
Sprinkle the remaining crumble mixture over the cherry layer without pressing, allowing some cherry filling to show through. Bake for 35–40 minutes or until the top turns golden brown.
Remove from the oven and let the Cherry Crumb Bars cool completely to room temperature.
Slice using a clean knife and serve.