Break bitter chocolate into smaller bits and place in a heat resistant bowl. Bring the cream to the boil and pour into the bowl with chocolate. Mix well until the chocolate fully dissolves and set aside for 15 minutes.
After that add to the chocolate mixture butter and mix well to obtain a smooth paste. If the mixture is not hot enough and the butter does not melt heat on a water bath. Cover the bowl with film and put for ca. 3 hours into the fridge. When the paste has set add crushed wafers and mix gently with a spatula. Divide the paste into portions with a spoon, put on a baking sheet lined with paper and return to the fridge for 10-15 minutes. After that remove from fridge, coat the portions in cocoa powder and form into balls. Return truffles again to the fridge for 10-15 minutes. In the meantime melt the rest of the chocolate in a water bath and leave to cool down. Dip cold truffles in the chocolate and set aside on parchment for the chocolate to set.
Dust with favourite sprinkles.