Preheat oven to 425°. Line a baking sheet with parchment paper. In a bowl, stir together flour, brown sugar, baking powder, baking soda, and salt. With a pastry blender or two knives, cut in butter until mixture resembles coarse meal. Stir in chocolate chips. Make a well in the center and add buttermilk, egg, and vanilla. Stir just until combined, taking care to not overmix.

Transfer dough to a lightly floured work surface and knead 5 or 6 times. Pat into an 8'' circle and cut into 8 wedges. Transfer to prepared baking sheet, about 1-1/2'' apart. Brush each wedge of dough lightly with milk. Then bake until scones are golden brown, 12 to 15 minutes. Let cool on pan for 5 minutes before removing to a wire rack to cool completely.