Heat the oven to 375F. Line an 8x8 pan with parchment paper.
Place the nuts in a dry skillet over medium heat. Cook for 4 to 5 minutes, until golden and fragrant stirring often.
¼ cup sliced almonds
In the bowl of a food processor, combine the flour, brown sugar, granulated sugar, salt, and lemon zest. Pulse to combine.
2 ¼ cup all purpose flour, ½ cup light brown sugar, packed, ¼ cup (50g) granulated sugar, ½ teaspoon fine sea salt, 2 teaspoons lemon zest
Add the butter cubes to the flour mixture. Pulse until the mixture starts to clump together but is still sandy.
1 cup unsalted butter, cold, cut into cubes
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 and almonds 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. Keep refrigerated until ready to use.
¼ teaspoon cinnamon
Place the blackberries, lemon juice, and sugar in a medium bowl. Toss to combine. Let the blackberries sit and macerate while the crust cools.
2 ½ cups fresh blackberries, halved, 1 tablespoon lemon juice, ½ cup granulated sugar
When the crust is just warm, add the cornstarch to the blackberry mixture and mix until combined.
1 ½ tablespoons cornstarch
Pour the blackberry filling onto the crust.
Evenly sprinkle the crumb topping over 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.