Gather the ingredients. Make sure the butter is out if the fridge for a little bit, so that it gets soft. For the cocoa powder, I really like a rich black variety, such as this Guittard Cocoa Noir.
Preheat oven to 350°F. Get out a large baking sheet, and use a silpat or butter and flour it.
In a bowl whisk together flour, cocoa powder, baking soda, and salt.
Using a electric mixer, beat together the butter and granulated sugar until light and fluffy.
Add eggs and beat until combined well.
Stir in flour mixture.
It will get dark and form a stiff dough.
Stir in walnuts and mini chocolate chips.
On the baking sheet with clean, floured hands form the dough into two slightly flattened logs, each 12 inches long and 2 inches wide.
Sprinkle with the confectioners' sugar.
Bake logs 35 minutes, or until slightly firm to the touch.
Cool biscotti on baking sheet 5 minutes.
Transfer to a cutting board.
Use a serrated knife to cut biscotti diagonally into 3/4-inch slices.
Arrange biscotti, cut sides down, on baking sheet.
Put back in the oven and bake until crisp, about 10 minutes.
Cool biscotti on a wire rack.
Serve immediately, or keep in an airtight container for up to 1 week. You can also freeze for up to 1 month.