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, vanilla and egg. 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.
for the peanut butter glaze:
After removing the scones from the oven, prepare the glaze. In a glass measuring cup, whisk together all glaze ingredients until smooth. When the scones are mostly cooled (they can be slightly warm yet), drizzle the peanut butter glaze over the scones. I put this in the microwave for 30 seconds 2 or 3 times to help it smooth out nicely.
I believe scones are always best the day they are baked. But this recipe does allow for some advance prep. The unbaked dough freezes really well, enabling you to store the unbaked scones in your freezer and bake them up fresh when desired. Just cut the dough into wedges, place them on a tray in the freezer for an hour and then transfer the frozen wedges to a plastic freezer bag. On the day you want to bake them, take them directly from freezer to baking sheet lined with parchment paper (do not thaw first) and brush with milk. You will need to bake the frozen dough a bit longer, adding about 4 or 5 minutes onto the regular baking time.