Heat oven to 350 F. Line an 8-inch square baking pan with parchment paper.

In a large mixing bowl, whisk together butter, brown sugar, and fresh lemon zest thoroughly.

Add flour, baking soda, salt, and cinnamon and mix until the dry ingredients are well incorporated into the butter and sugar.

Take one cup of the crumble mixture and set aside for later.

Press the rest of the dough into the bottom of the prepared pan and bake for 12-15 minutes. Let the crust cool completely on a cooling rack.

In a medium mixing bowl, combine sugar, flour, blackberries, lemon zest, and lemon juice, mixing well.

Pour blackberry mixture on the cooled crust, and spread evenly across the top of the crust.

Sprinkle the remaining crumble topping over the blackberry filling.

Bake the blackberry crumb bars for 30-35 minutes or until golden brown.