Most chocolate sauces are made by combining melted chocolate with varying proportions of heavy cream, butter, egg yolks, or other liquids. The amount of each of these ingredients depends on the desired consistency of the sauce and whether the sauce is being served hot or cold.
Bittersweet (sometimes called semisweet) chocolate is the type of chocolate most often called for in chocolate sauce recipes, but other chocolates can be substituted and the recipe modified if bittersweet is unavailable. Always use the best-quality chocolate.