Preheat your oven to 375°F (190°C). If using frozen blackberries, allow them to thaw slightly. In a medium bowl, toss the blackberries with ½ cup of sugar and let them sit for 10 minutes to release their natural juices.
In another bowl, whisk together flour, remaining sugar, baking powder, salt, and cinnamon (if using). Stir in the milk, melted butter, and vanilla extract until you get a smooth batter.
Pour the batter into a greased 9×13-inch baking dish. Evenly distribute the blackberries and their juices over the top. Don’t stir—this helps create that classic cobbler texture!
Bake for 40–45 minutes, or until the cobbler is golden brown and bubbling. The batter will rise around the blackberries, creating a beautiful crust.
Allow the cobbler to cool slightly before serving. Enjoy it warm with whipped cream or a scoop of vanilla ice cream.