1. Combine blackberries and granulated sugar. Let stand at least 30 minutes.
2. Preheat oven to 400F. Line a baking sheet with parchment paper.
3. Combine flour, pecans, brown sugar, baking powder and salt in a large mixing bowl. Add butter and using your fingers or a fork, cut butter into the flour mixture until it resembles coarse meal. Add vanilla and milk.
4. On a lightly floured cutting board, pat dough into a 5 x 9-inch rectangle, 3/4-inch thick. Cut into 8 pieces. Sprinkle turbinado sugar on top.
5. Place shortcakes on baking sheet and bake 15-18 minutes, until puffed and lightly colored. Cool on a wire rack.
6. Slice shortcakes into halves horizontally; spoon blackberries and juice between halves and top with whipped cream, if using.