In a large bowl, whisk together flour, ⅓ cup sugar, baking powder, salt, and orange zest. Using a pastry blender, cut in butter until mixture is crumbly.
In a small bowl, whisk together egg, ⅓ cup milk, and vanilla. Stir egg mixture into flour mixture just until dry ingredients are moistened; gently stir in blackberries. (Dough will be crumbly.)
Using floured hands, gently pat dough into a 7-inch square on parchment-lined pan. Cut dough in half lengthwise and widthwise to make 4 squares. Cut each square diagonally to create 8 triangles. Gently separate dough pieces slightly on pan. Freeze for 15 minutes.
Preheat oven to 375°. Spray a 12-inch square cast-iron griddle or 15-inch round cast-iron baking pan with cooking spray.
Place cold dough pieces on prepared pan, leaving a slight space between each. Brush remaining 1 tablespoon milk onto scones; sprinkle with remaining 2 tablespoons sugar.
Bake until lightly browned, 20 to 25 minutes. Let cool for 20 minutes; serve warm.
Recipe by Southern Cast Iron at https://southerncastiron.com/blackberry-scones/