Begin by preheating your oven to 375°F (190°C) and lightly butter or grease a 9-inch baking dish.

In a large bowl, combine the fresh blackberries, ¾ cup granulated sugar, lemon juice, cornstarch, vanilla extract, and optional cinnamon.

Pour the berry mixture into your prepared baking dish and spread evenly.

In a separate bowl, whisk together the flour, ½ cup granulated sugar, baking powder, baking soda, and salt.

Add the cold, cubed butter to your dry ingredients and cut it into the mixture until it resembles coarse crumbs.

Stir in the buttermilk until just combined.

Drop spoonfuls of dough over the blackberry mixture.

If using, sprinkle coarse sugar over the dough topping.

Bake in your preheated oven for 35 to 40 minutes until the topping is golden brown and the filling is bubbly.

Allow to cool slightly before serving.