Begin by preheating your oven to 350°F (175°C). This ensures your cobbler starts baking evenly right from the beginning. A hot oven is crucial for that perfect crust.

Wash your blackberries under running water. Once clean, gently pat them dry. Place them into a medium-sized bowl, and toss them with 1/4 cup of sugar, allowing the fruit to settle for about 10 minutes. This draws out the juices, which enhances the flavor of the cobbler.

In a separate large bowl, whisk together the all-purpose flour, baking powder, salt, and ground cinnamon. It’s essential to blend these before adding wet ingredients. This step ensures an even distribution of the baking powder throughout your mix.

In another bowl, combine the melted butter (though it should be cooled slightly) with the remaining granulated sugar and vanilla extract. Mix until well incorporated. The result should be creamy and smooth, which creates a delightful base for our cobbler.

Now, add the milk (or heavy cream) gradually to your butter and sugar mixture, stirring gently. Then fold in the dry ingredients until just combined. It’s okay if the mixture looks slightly lumpy; overmixing can lead to a tough cobbler.

In a greased baking dish, pour in the blackberries along with their juices. Spoon the batter over the top of the berries. Do not stir; you want them to remain at the bottom, creating that fruity layer.

Place the dish in the preheated oven and bake for 45 to 55 minutes. The top should turn golden while the berries bubble away, creating a mouthwatering sight that means one thing: it’s almost time!

Let your cobbler cool for about 15 minutes before serving. This waiting period allows the filling to set a bit, which helps each serving hold together wonderfully.