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 well blended.
03 - Add cold butter cubes to the flour mixture. Use a pastry cutter or fingers to work butter into flour until mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - Stir in chocolate chips until evenly distributed throughout the flour-butter mixture.
05 - In a separate bowl, whisk together heavy cream, egg, and vanilla extract until fully combined.
06 - Pour wet ingredients into dry ingredients. Gently mix with a fork until just combined and dough begins to come together. Do not overmix.
07 - Turn dough onto lightly floured surface. Gently pat into a 1-inch thick circle, about 8 inches in diameter. Cut into 8 equal wedges and transfer to prepared baking sheet.
08 - Brush tops of scones with a little extra heavy cream. Bake for 16-18 minutes until golden brown and cooked through. Cool on wire rack.
09 - Whisk together powdered sugar, milk or cream (start with 2 tablespoons), and vanilla until smooth and pourable. Add more liquid if needed to reach desired consistency.
10 - Drizzle glaze over completely cooled scones. Allow glaze to set for 10-15 minutes before serving.