Preheat oven to 350 degrees
Using a stand or electric mixer, combine cake mix, melted butter, eggs, flour, and nuts until well blended.
Transfer dough to parchment paper-lined baking sheet and spread with hands until dough is rectangular in shape and 1/2" thick.
Bake 30-35 minutes or until a toothpick inserted in the center comes out clean.
Remove from oven and allow to cool 10 minutes
Use a bread knife to slice rectangle diagonally into 1" thick slices
Arrange slices back on the baking sheet and bake for another 10 minutes
After 10 minutes, turn the oven off and allow biscotti to remain in the oven until crisp (about 30 minutes)
Transfer to wire baking rack to cool completely.