Start by preheating your oven to 400°F. In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.

Grate the cold butter using a cheese grater for easy incorporation into the dry ingredients. If a grater isn't available, cut the butter into small cubes. Use a pastry cutter or two knives to blend the butter into the flour mixture until it resembles coarse crumbs. Gently fold in the blackberries.

Combine the buttermilk and vanilla extract in a small measuring cup. Stir this mixture into the flour mixture until just combined, being careful not to overmix to keep the scones light and fluffy.

Lightly flour a clean surface and knead the dough briefly. Shape the dough into a circle about 1 1/2 inches thick. Cut the circle in half, then cut each half into 4-5 wedges, depending on your preferred scone size.

Place the scone wedges on a baking sheet lined with parchment paper. Brush the tops with a bit of milk and sprinkle with a touch of sugar for a golden finish.

Bake in the preheated oven for 20-22 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean. Allow the scones to cool on a wire rack before serving.