Preheat oven to 400 degrees F (205 degrees C). Lightly butter a 9 inch diameter circle in the center of a baking sheet.
In a large bowl, stir together flour, brown sugar, baking powder, baking soda, and salt. Cut the butter into 1/2 inch cubes, and distribute evenly over flour mixture. With a pastry blender or two knives, cut butter into the flour mixture. Stir together buttermilk, egg, and extract; add to the flour mixture, and stir to combine. Stir in the chocolate chips and hazelnuts. The dough will be sticky.
Spread the dough into an 8 inch diameter circle on the baking sheet. Cut with a serrated knife into 8 wedges.
Bake for 17 to 19 minutes, or until the top in lightly browned. Cool on baking sheet for 5 minutes. Transfer scones to the wire rack to cool, and cut into wedges. Serve warm, or cool completely and store in airtight container.
