Preheat your oven to 375°F (190°C) and prepare an 8-inch round cake pan by buttering it or lining it with foil.

In a medium bowl, combine fresh blackberries, lime juice, granulated sugar, cinnamon, salt, and cornstarch. Toss gently and set aside.

In a large bowl, whisk together all-purpose flour, sugar, and salt. Cut in cold butter until mixture resembles coarse crumbs.

Press the remaining mixture into the bottom of the prepared pan and poke small holes in it with a fork.

Layer the blackberry filling over the crust, leaving behind any excess juice, then sprinkle the reserved crumb mixture on top.

Bake for 20 minutes on the lower rack, then move to the top rack for 10-15 minutes until golden brown.

Cool at room temperature and then refrigerate for at least 90 minutes before slicing.