01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt until evenly blended.
03 - Add cold cubed butter to dry mixture. Using pastry cutter or fingertips, work butter into flour until mixture resembles coarse crumbs with pea-sized butter pieces remaining.
04 - In small bowl, whisk together buttermilk, egg, and vanilla extract until combined.
05 - Pour wet ingredients into dry mixture. Mix gently with spatula or wooden spoon until just barely combined. Dough should appear shaggy and slightly sticky.
06 - Fold chocolate chips into dough gently, taking care not to overmix.
07 - Turn dough onto lightly floured surface. Pat into 1-inch thick circle using hands. Cut circle into 8 equal wedges using sharp knife or bench scraper.
08 - Place wedges on prepared baking sheet, leaving 2 inches of space between each scone to allow for spreading.
09 - Bake 16-18 minutes until tops are golden brown and scones are set. Transfer to wire rack to cool completely.
10 - Whisk powdered sugar, 2 tablespoons milk, and vanilla extract in small bowl until smooth. Add remaining tablespoon milk if needed for pourable consistency.
11 - Drizzle glaze generously over completely cooled scones. Allow glaze to set for 10 minutes before serving.