Line an 8 by 8 square pan with aluminum foil.
You want to make your two different fudges at the same time. So put two medium sauce pans over medium low heat. Add the peanut butter chips, peanut butter and half the sweetened condensed milk to one. Add the chocolate chips, Nutella, and the rest of the sweetened condensed milk to the other.
With two sepearate spoons, stir each saucepan, until the ingredients in each are melted and smooth.
Remove them from the heat, and working small scoops at a time, alternate between adding the Nutella and the peanut butter fudge to the pan.
Once finsihed, for a more marbled look, you can run a knife through the fudge, though mine set pretty quickly and saw very little knife action but still had a nice marbled look once cut.
Let set at least four hours, I let mine set overnight. Remove from the pan, cut and serve.