Heat the oven to 375F. Line an 8x8 pan with parchment paper.
In the bowl of a food processor, combine the flour, granulated sugar, brown sugar, salt, and lemon zest. Pulse to combine.
Add the butter cubes to the flour mixture. Pulse until the mixture starts to clump together but is still sandy.
Remove 1 cup of the mixture, and turn out the remaining mixture into the prepared pan.
Lightly press the dough evenly into the pan. Bake the crust for 20-25 minutes, or until light golden brown.
Add the cinnamon to the reserved 1 cup of the flour mixture and combine. Use the tips of your fingers to squeeze the dough together to make clumps for the topping. You don't want this part to be sandy.
Add the almonds (or you can wait to sprinkle them on at the before baking), and place the crumbs into the refrigerator to keep chilled.
Place the blackberries, lemon juice, and sugar in a medium bowl. Toss to combine. Let the blackberries sit and macerate while the crust cools.
When the crust is just warm, add the cornstarch to the blackberry mixture and mix until combined.
Pour the blackberry filling onto the crust.
Evenly sprinkle the crumbs and almonds on top of the blackberry filling.
Bake the bars for 35-45 minutes, until the blackberries and juices are bubbling around the edges and the topping is golden brown.
Allow the bars to cool completely before serving.