Preheat your oven to 375°F (190°C). Grease a 9x13 inch baking dish.
In a large bowl, combine the blackberries, 0.75 cup sugar, 0.25 cup flour, lemon juice, and cinnamon. Toss gently to coat the berries. Pour the blackberry mixture into the prepared baking dish.
In a separate medium bowl, whisk together 1.5 cups flour, 0.75 cup sugar, baking powder, and salt.
Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs.
Pour in the milk and stir just until combined. Do not overmix.
Spoon the cobbler topping evenly over the blackberry filling.
Bake for 35-45 minutes, or until the topping is golden brown and the filling is bubbly. If the topping starts to brown too quickly, you can loosely tent it with foil.
Let the cobbler cool for at least 15 minutes before serving. Serve warm, perhaps with a scoop of vanilla ice cream.
Notes
This cobbler is best served warm, ideally with a dollop of whipped cream or a scoop of vanilla ice cream. For an extra special touch, sprinkle a little turbinado sugar on top of the cobbler before baking for a little sparkle and crunch.