Preheat your oven to 350°F (175°C). Butter a 9×13-inch baking dish well.
In a medium bowl, gently toss blackberries with sugar and lemon juice. Let them sit while making the batter.
In a large bowl, whisk together flour, sugar, baking powder, and salt.
Stir in milk and melted butter until just combined; don’t overmix.
Pour the blackberry mixture into the prepared dish and spread evenly.
Drop spoonfuls of batter over the blackberries.
Baking
Bake for 45–50 minutes until the top is golden.
Let the cobbler rest for 10–15 minutes before serving.
Notes
Cool leftovers to room temperature, then store in the refrigerator for up to 3–4 days. For longer storage, freeze tightly wrapped, then thaw and reheat as needed.