Preheat your oven to 400°F (200°C) and butter an 11-inch oval baking dish.

Combine all dry dough ingredients in a food processor, then add cold butter and pulse until it resembles coarse crumbs.

Mix milk and vanilla in a separate bowl, then pour into the processor while pulsing until a cohesive dough forms.

Lightly flour a countertop, knead the dough a few turns, and roll it out into a rectangle approximately 18x12 inches.

In a bowl, toss blackberries with sugar and cornstarch, then spread over the rolled dough.

Roll the dough tightly from one long edge, cut into 8 equal pieces, and place in the prepared dish.

Bake at 375°F (190°C) for 35-40 minutes until golden brown.

Whisk melted butter, confectioner's sugar, salt, and milk in a bowl for the glaze, then drizzle over warm rolls.