Preheat oven to 425°F, with a rack in the upper-middle position. Line a baking sheet with parchment paper.

In a small bowl whisk buttermilk and egg. Set aside.

In a large bowl, combine flour, sugar, baking powder and salt. Scatter butter pieces over the flour. Using your fingertips (or a pastry cutter), work the butter into the flour by rubbing it quickly into small pieces. Proceed until the mixture resembles a sandy texture with pebble-sized pieces of butter (the pieces of butter will be irregularly shaped; that's fine). Stir in the chocolate chips.

Reserve 1 tablespoon of the buttermilk-egg mixture (this will be for brushing the top of the scones), pour the remaining buttermilk mixture into the flour, along with the vanilla extract. Use a rubber spatula or wooden spoon to stir the dough until it starts to come together. Once it’s almost all the way combined, dump the dough onto a floured work surface and knead it a couple of times until it comes together. Pat the dough into a ¾ inch thick circle or rectangle. Cut into desired shapes (I made 12 triangles).

Place the scones on the baking sheet. Brush the tops with the reserved buttermilk, sprinkle with coarse sugar.

Bake for 11-14 minutes, until the bottoms are beginning to brown and the tops are light golden brown. Place the baking sheet on a wire rack to cool.

Whisk ingredients in a small bowl until combined. Adjust the consistency by adding a little more powdered sugar (to thicken) or cream (to thin). Drizzle over the slightly cooled scones.