Temper chocolate, add cream in thirds, add cold butter and whisk a while. Chill, then scoop balls (it's best to already use a melon scoop or small ice cream scoop here) and chill them again. Shape into proper balls (I didn't do this in the photo), then chill again.
Temper another batch of chocolate, dump truffles in it and roll between your gloved hands (like this you'll get a very thin layer of coating). Toss into powder, then sieve exzess off.
My current favourite is using a fine olive oil as flavour, covering them in white chocolate and tossing them in 抹茶 powder. I find cocoa a bit obvious. I tried also きな粉, but that doesn't add much. The 抹茶 adds very little taste, so it really needn't be the highest grade, but it looks very nice.