Things You'll Need
Chocolate is a temperamental ingredient as it is sensitive to changes in the proportion of cocoa solids to cocoa butter it contains. For example, adding alcohol -- which comprises at least 35 percent of peppermint extract -- causes chocolate to seize and form clumps unless you incorporate an additional fat such as cream or butter. However, you can add peppermint oil -- a pure form of flavoring squeezed from peppermint plants -- directly to chocolate without any problems.
Chop the dark chocolate into fine pieces and set it aside.
Heat heavy cream in a heavy-bottomed saucepan over medium-low heat. Use 2 parts chocolate to 1 part cream -- by weight, not volume -- for a dense, truffle-like consistency; use equal parts chocolate and cream for a thick, spreadable glaze; use 2 parts cream to 1 part chocolate for a pourable icing or glaze.
Stir the chocolate into the heavy cream until it melts. Add 2 drops of peppermint extract per pound of chocolate. Stir to incorporate the extract.
Chop the chocolate. Melt it in a double boiler over medium-low heat. Alternatively, melt the chocolate in a mixing bowl set over a saucepan of hot water.
Add 1 drop of peppermint oil per 1/4 pound of chocolate.
Stir the oil into the chocolate for 1 full minute. Lower the heat to "Warm" to hold the chocolate until needed.
You can add 1 tablespoon of butter per 1/4 pound of melted chocolate instead of cream to prevent the chocolate from seizing.