Chop chocolate bar into fine pieces and place in a heat-proof bowl.
In a small saucepan, heat heavy cream until it just begins to simmer. Pour hot cream over the chopped chocolate and place a plate over the top of the bowl to trap the heat. Allow to set for 2-3 minutes or until chocolate has softened completely.
Whisk together the cream and melting chocolate until a smooth, glossy ganache forms. If some chunks of chocolate remain, you can microwave the mixture for 15-30 seconds until fully melted and smooth.
Add the peanut butter to the ganache mixture and stir or whisk until completely combined. Press a piece of plastic wrap onto the ganache and place in the refrigerator for two hours to harden.
When ganache is solid all the way through, use a melon baller to form 1½ tablespoon size scoops of the ganache. Roll between the palms of your hands to form a round ball and place on a piece of parchment paper.
Place the truffle balls back into the refrigerator or freezer to harden after handling them (about 30 minutes).
Place the chopped peanuts and the cocoa powder into separate shallow bowls.
Roll chilled truffles, one at a time, in desired coating. Be sure to coat the entire truffle.
Keep cool until ready to serve.