Combine flour, brown sugar, baking powder, salt, and instant espresso powder in a large bowl.
Cut the cold butter into the dry ingredients until coarse crumbs form, then stir in the mini chocolate chips.
Whisk together the vanilla extract and cold heavy cream, then pour into the flour mixture in two parts and mix gently.
Turn the dough onto a floured surface, knead gently, and shape into an 8-inch circle.
Cut the dough into eight triangles, place on a baking sheet, and refrigerate for 30 minutes to an hour.
Preheat oven to 400°F, brush scones with egg wash, sprinkle with turbinado sugar, and bake for 20-25 minutes.
Prepare the coffee glaze by mixing sifted powdered sugar with instant espresso, brewed coffee, and cream until smooth.