Chocolate bars chopped into small chunks can also be used. Try to use dark chocolate.
I divided the ganache into two parts, I added rum in one and formed it into rocks. The other batch I kept alcohol free.
If you are in a hurry put the ganache in the freezer for 30-40 minutes and start shaping. Don't let it get too hard or giving it a shape will be difficult.
This can be stored in an airtight container in the refrigerator for up to 2 weeks.
If you divide the ganache into two parts, use 2 teaspoon of rum instead of 4, and add more as needed after tasting.