Preheat your oven to 350°F (175°C). Lightly grease your 9-inch baking dish with melted butter.
In a medium bowl, whisk together 1 cup all-purpose flour, ½ cup cane sugar, 1 teaspoon baking powder, and ½ teaspoon sea salt.
In another bowl, mix 1 cup milk, 4 tablespoons melted unsalted butter, and 1 teaspoon vanilla extract until well combined.
Pour the wet ingredients into the dry ingredients and stir gently with a wooden spoon or spatula until just combined. Avoid overmixing.
Spread the heaping 2 cups of fresh blackberries evenly across the bottom of the prepared baking dish.
Carefully pour the batter over the blackberries, covering them as evenly as possible.
Sprinkle a little extra cane sugar over the top of the batter.
Bake for 45-50 minutes, or until the topping is golden brown and a toothpick inserted into the biscuit layer comes out clean.
Remove from oven and let cool for about 10 minutes. Serve warm with vanilla ice cream.
