Using a countertop mixer, add the butter, sugar, salt, vanilla, and baking powder. Mix on medium-low speed until mixture is fully combined and smooth.

Add the eggs and milk; mix on low speed until fully absorbed.

Add the flour, cocoa powder and chopped walnuts and mix on low speed until fully combined.

Transfer dough to a lined baking sheet and shape into a 6"x10" log.

Bake at 350°F for 25 minutes.

Remove pan from oven and allow it to cool for 7-8 minutes. Transfer biscotti to a cutting board and use a sharp knife to slice the log crosswise into 3/4" slices. Place each biscotti cut-side down on a lined-baking sheet.

Reduce oven temperature to 325°F and continue baking for another 28-30 minutes, or until the biscotti turn crispy on the cut edges. (Tip: Pull the pan out of the oven and carefully press on one of the cut edges. It should be fairly hard and crispy. If you’re able to press down, then return the pan to the oven and continue baking several more minutes.)

{Optional} Once biscotti have fully cooled, dust tops with powdered sugar.