In a 9″ baking dish, toss together the blackberries, sugar, cornstarch, lemon zest, and lemon juice. Set aside for 30 minutes for the berries to macerate and sugar to dissolve.
4 cups (18oz) blackberries, 1/2 cup (100g) granulated sugar, 2 Tbsp cornstarch, zest of 1 lemon, 1 Tbsp lemon juice
After 15 minutes, preheat oven to 350F and start on the biscuits.
Whisk together the flour, sugar, baking powder, and cinnamon in a medium bowl.
1 cup (125g) all-purpose flour, 1/4 cup 50g granulated sugar, 1 1/2 tsp baking powder, 1/2 tsp ground cinnamon
Cut in the butter until the mixture resembles coarse crumbs.
4 Tbsp (57g) unsalted butter
Add the buttermilk and stir until just combined. Dollop large spoonfuls of dough on top of the berries.
1/2 cup (125ml) buttermilk
Bake for 30-40 minutes or until the filling is bubbling and the biscuits are golden brown.
Notes
Leftovers can be tightly covered and stored in the fridge for 3-4 days.