1. Beat butter and sugar at medium speed with an electric mixer 2 minutes or until light and fluffy. Add egg, beating until smooth, stopping to scrape down sides as needed. Stir in vanilla and espresso powder.
2. Stir together flour, baking soda, and salt. Gradually add to butter mixture, beating at low speed until blended. Stir chopped bittersweet chocolate and chopped hazelnuts into batter. Drop by rounded tablespoonfuls 2 inches apart on lightly greased or parchment paper-lined baking sheets. Bake, in batches, at 350° for 10 to 12 minutes. Let cool completely on wire racks.