12 ounces semi sweet chocolate chips
12 ounces heavy (whipping) cream
1 T butter
I got these instructions from LIZ W in ladycakes.com. This method has never failed me.
In a double boiler place all ingredients. If you are adding flavoring such as a liqueur, now is the time to add it also.
Leave on low heat until chips are melted. Stir gently with a spoon (no whisks used here!!) until chips are melted. At first you will think you messed up because it will be very ugly, but be patient. It will all come together soon!! At this point it will look sort of curdled or lumpy. Keep stirring gently. Be careful not to get air bubbles in to your mixture.
Keep stirring the mixture very slowly until the ingredients are a thick, dark, glossy chocolate. You will still have some streaks of cream that haven't fully mixed in and some small lumps of soft chocolate that you can't smooth without adding air bubbles. Don't worry. I promise.
OK- now comes the fun part. Using a "boat motor" mixer (I will attach a picture), hold the head below the surface of the ganache and mix to remove the final lumps. It's very important you keep the boat motor below the top of the chocolate mix at all times. If the boat motor mixer does not submerge in the chocolate, place the chocolate in a smaller bowl. But get that head under the ganache!! Other wise you will have bubbles!
Now, you will allow the mixture to cool to body temperature. You must allow it to cool to pour properly. Don't worry, it will be pourable for quite a long time after coming to body temperature. The cooling process can take up to an hour or even more, depending on your room conditions. You can remove the top pan of the double boiler and place on the counter for fasting cooling. Don't worry if your ganache develops a skin. You can gently mix it back in after cooling.
I now place my cake on a board a hint smaller than my cake. I ice the cake in buttercream (usually chocolate) with a 1/4-inch layer. I make sure my edges are crisp and sharp. Your ganache is only as good as what is beneath it. Don't pour the ganache onto an uniced cake. You will have lumps and runs!! Place the iced cake in the fridge for at least 1 hour. Do not freeze!!
Place the cold cake (still on it's small board) on a cooling rack which has been placed over a jelly roll pan. In one continuous motion, pour over the cake. If you have to stop and start over, you will have runs and streaks. I find doing this portion of the cake is easier when the cake is sitting no higher then my waist. This way I can see that I got all around the cake. Start pouring in the middle of the cake and swirl your way out to the edges. Don't worry about the wasted ganache running on to the jelly roll pan. It's all reusable.
Transfer the covered cake onto another cooling rack over another jelly roll pan. Place the cake still on the jelly roll pan in to the fridge. Leave for at least 10-15 minutes.
Once the ganache is set you can place your cake on the presentation board and finish decorating.