Triple Berry Crumble Bars

Preheat the oven to 375℉ (190℃). Spray a 9×9 inch pan with non-stick spray and line it with parchment paper.
Add the sugar and lemon zest to a large bowl. Rub the lemon zest and sugar together with your fingertips to extract the most lemon flavor from the zest.
1 1/4 cups (250 g) granulated white sugar, 1 tbsp (10 g) lemon zest
Add in the softened butter and vanilla. Cream together with an electric mixer on high speed for 1-2 minutes until very light and fluffy.
1 cup (224 g) unsalted butter, softened, 1 tsp vanilla
Add in the flour and salt. Mix on low speed just until combined. The dough should form into large clumps.
2 1/2 cups (312 g) all purpose flour, 3/4 tsp salt
Set aside 1/3 of the dough for the crumble, and use 2/3 of the dough for the crust.
(If you want to be very precise, use a kitchen scale to weigh the entirety of the dough and divide by three so you know exactly how many grams of dough should be used for the topping! :) )
Chill the portion of dough reserved for the crumble in the fridge while working on the rest of the bars.
Press the larger portion of dough into the bottom of the prepared 9x9 inch pan. A small offset spatula really helps to smooth out the dough into one even layer.

Add the raspberries, blueberries and blackberries to a large bowl.
1 3/4 cups (232 g/ 8 oz.) fresh raspberries, 1 1/2 cups (240 g/ 8.5 oz.) fresh blueberries, 1 3/4 cups (250 g/ 9 oz.) fresh blackberries
Add in the sugar, cornstarch, lemon zest and lemon juice. Gently toss with a spatula to coat the berries. Let the berries sit for a few minutes to absorb the cornstarch and make a bit of a juice.
3/4 cup (150 g) granulated white sugar, 1/4 cup (32 g) cornstarch, 1 tbsp (10 g) lemon zest, 1 tbsp (15 ml) lemon juice
Then, pour berry filling over the crust.
Remove the crumble from the fridge and sprinkle it evenly over the berries.
Bake the bars for 65-70 minutes, or until they're golden brown on top and the berry filling is bubbling.
Let the berry crumble bars cool completely on a wire rack before cutting to ensure the filling has time to firm up. Once cooled, cut into 16 bars and enjoy!