Line a loaf pan with parchment paper. Make sure you have a place for it in the freezer.
Combine chocolate chips and nut butter in a saucepan and warm over low heat. Stir frequently until chocolate chips are completely melted and mixture is fully combined.
Pour mixture into prepared pan and put in the freezer for about 1 hour or until firm. To prevent cracking, allow fudge to rest on counter for 10 minutes after freezing to soften slightly before slicing.