Preheat oven to 350 degrees F and butter and flour a large baking sheet.
In a bowl whisk together flour, cocoa powder, baking soda, and salt. In another bowl with an electric mixer beat together butter and granulated sugar until light and fluffy. Add eggs and beat until combined well. Stir in flour mixture to form a stiff dough. Stir in hazelnuts and chocolate chips.
On prepared baking sheet with floured hands from dough into two slightly flattened logs, each 12 inches long and 2 inches wide, and sprinkle with confectioners' sugar. Bake logs 35 minutes, or until slightly firm to the touch. Cool biscotti on baking sheet 5 minutes.
On a cutting board cut biscotti diagonally into 3/4-inch slices. Arrange biscotti, cut sides down, on baking sheet and bake until crisp, about 10 minutes. Cool biscotti on a rack Biscotti keep in airtight containers 1 week and , frozen, 1 month.
