In a bowl, whisk together flour, cocoa powder, baking soda and salt.
In another bowl with an electric mixer beat together the butter and granulated sugar until light and fluffy. Add eggs and beat until mixed well. Stir in flour mixture to form a stiff dough. Stir in walnuts and chocolate chips.
On the prepared baking sheet with floured hands, form dough into two slightly flattened logs, each 12 inches long and 2 inches wide, and sprinkle with confectioners' sugar. Bake logs for 35 minutes, or until slightly firm to the touch. Cool biscotti on the baking sheet for 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. Keep the biscotti in air-tight containers for 1 week and, frozen, 1 month. Yields 30 biscotti.