Line a loaf pan (or similar sized pan) with parchment paper.
To make the chocolate batter, start by mixing the whey powder with the cocoa.
Add the water, and mix well.
Add the almond butter and salt. Mix well.
Spoon the batter into the pan, and set aside.
To make the peppermint batter, start by mixing the whey powder with the water.
Add peppermint extract and agave. Mix well.
Add coconut flour. Mix well.
Spoon peppermint batter on top of chocolate batter in pan. (Do not cover all of the chocolate batter.)
Use the back of a butter knife to swirl the fudge batters.
Freeze for several hours, until the parchment peels cleanly from the fudge.
Cut into squares, and enjoy! Store in the freezer.
Notes
A note about substitutions: Casein or a whey/casein blend can be substituted for the whey powders (although you may need more water), and other sweeteners for the agave.