Preheat the Oven: Set your oven to 400°F. Line a baking sheet with parchment paper for easy cleanup.
Prep the Vanilla Beans: Slice the vanilla beans lengthwise, carefully scraping out the seeds with the back of your knife. Combine the seeds with granulated sugar in a large mixing bowl.
Mix Dry Ingredients: Add the all-purpose flour, baking powder, and salt to the vanilla sugar mixture. Whisk to combine.
Chill the Mixture: Place this dry ingredient mixture in the freezer for 10 minutes. This helps maintain a cold temperature, which is essential for flaky scones.
Add Butter: Remove the bowl from the freezer and add the cold butter cubes. Use a pastry cutter or your fingertips to incorporate the butter until the mixture resembles coarse crumbs.
Prepare the Wet Ingredients: In a separate bowl, whisk together the sour cream, 6 tablespoons of heavy cream, and vanilla extract until smooth.
Combine Wet and Dry Ingredients: Pour the wet mixture into the dry ingredients, mixing gently with your hands until it forms a rough dough. If the dough is too dry, add 1 tablespoon of cream at a time.
Fold in Blackberries: Gently incorporate the frozen blackberries, ensuring they are evenly distributed without crushing them.
Shape the Scones: Lightly flour a clean surface and shape the dough into a 9-inch circle. Use a sharp knife to cut the dough into 8 equal wedges. Arrange the wedges on the prepared baking sheet, leaving space between them.
Brush and Bake: Lightly brush the tops with additional cream. Bake for 22 to 25 minutes or until the scones are lightly golden around the edges.