Chocolate scorches easily, so always melt it over hot - not boiling - water. It is best to use a double boiler, but you can improvise by using a c or bowl in a small saucepan over very gentle heat. The water must be kept below simmering to prevent steam from curling up and hitting the chocolate. If steam gets into the melted chocolate it will immediately thicken the mixture to a stiff mass. If this does happen, however, you can rescue the chocolate by softening it again. To do this, add 1-2 tb of vegetable shortening (never use butter as it contains moisture which will cause the chocolate stiffen even more!) to the chocolate and stir vigorously. You can also melt chocolate directly over very low heat in a heavy gauge saucepan, but you must watch the mixture carefully.