Melt the dark chocolate in a double boiler or in the microwave. I melted mine in a microwave in a heatproof bowl on high for 30 seconds. Then I removed it and gave it a stir. Then back in the microwave on high for another 30 seconds, and so on until it was fully melted. This helps it not to get too hot and get those overly cooked crusty bits that can sometimes form.
Use a fork to dip the chilled balls (giggle—sorry, I have no class) in the melted chocolate. Gently tap the fork on the side of the bowl with the truffle on the end to remove excess chocolate. Place back on the lined plate. Immediately cover with sprinkles or crushed peppermints. These will set on their own, but to speed up the process just pop them in the freezer again.