Unlike cooking chocolate, eating chocolate does not need to be tempered. Melt it with care. The merest drop of water causes the chocolate to separate and become firm, grainy and unusable. Overheating has the same effect. Use a heatproof bowl that sits on top of a saucepan, not down inside it. This prevents any water or steam from entering the bowl.
Heat some water until barely simmering, then reduce the heat so that it cools a little. Leave the pan over a low heat or remove it from the hob before placing a bowl filled with pieces of chocolate on top. Make sure the pieces are broken into small, roughly equal sizes so the chocolate melts quickly in a smooth and even consistency.