Ganache (pronounced as ga-nash) is a French term meaning a smooth mixture of chocolate and cream. It is basically hot cream poured on chopped chocolate, allowing it to melt, then stirred till smooth. Additionally, butter or oil, honey or corn syrup and flavorings are added to the mixture. The emulsion is cooled to various degrees according to the preferred end consistency of the ganache.
The result is a glossy, smooth, uber delicious and creamy emulsion you could eat as is and if have any left over, use to frost your cake. This is a fabulous cake frosting if you have just begun baking, guaranteed to please most palates, making it a great confidence booster for a beginner. Its quite easy to prepare if you can lay your hands on good chocolate, some good cream and remember some basic rules, dos and don't 's while making this. You can't really go wrong with this unless you burn the cream or add cold flavoring to the ganache.
Here is some information for you, which I have majorly collected from Baking 911 and Joy Of Baking. And a couple of bits from what I have learnt (from my mistakes!), do correct me if I am wrong.
Chocolate : The chocolate here can be bittersweet or dark chocolate if you prefer a slightly bitter and less sweet frosting, milk chocolate for a sweeter frosting and white chocolate, well, if you like the taste of it. The taste depends on the quality of chocolate you use. Valrhona, Dove, Lindt and the kind are the preferred high end brands. I personally like ganache made with dark chocolate and use a brand called Morde (not high end by any stretch of imagination!) which is quite good. If you by any chance store the chocolate in the freezer or fridge, get it out, let come to room temperature, chop quite fine before using.
Cream : Whipping cream or heavy cream with a high butter fat content of 35-40% is supposed to be the best for a good, stable ganache. The only cream we get here is a low fat one with 25% butter fat, so its Amul Fresh cream for us. It works well, so am a happy user of the brand. I personally have not used the local fresh cream available at the supermarket, so can't really say how it will work. Sour cream or crème fraîche can also be used in place of cream. I have also used whipping cream (like Rich's) for making ganache a couple of times in an emergency, but it makes sweet ganache.
Proportion of cream to Chocolate : The proportion of cream and chocolate can vary according to personal preference and also the use for which the ganache is intended for. Equal weights of chocolate and cream is the preferred proportion. More of chocolate will give you firm ganache, less chocolate will give you a softer one. I use 1 1/4 cup of chocolate for one cup of cream, have never checked how much it weighs though. I use about 1 tablespoon of soft unsalted butter for this proportion. Do experiment with the proportions to figure out what you will like better. I prefer to use butter and not honey or corn syrup for the extra shine as using these will make the ganache sweeter.
Flavorings can be liqueur, extracts, coffee, citrus zest etc. You could also use spices like cinnamon, herbs like lavender etc to infuse into the cream when you heat. Strain it, re-heat if needed and continue with the process. You could add almond meal to ganache for nutty taste and some texture.
Getting Ready : Keep any refrigerated flavoring such as essence out of the fridge before you begin. This is to ensure it comes to room temperature when you add it to the ganache. This is very very important. In case you forget to do so, you are better off not adding cold flavoring lest you end up with a hard lump of chocolaty mass instead of good ganache.
You will need : A heavy bottomed saucepan, cream, chocolate, unsalted butter, a good heat-resistant spatula, a clean and dry bowl with a fine strainer suspended over it, cling film to cover the bowl as it cools. And of course any extract at room temperature if adding.
Cut the chocolate into pieces, very small ones preferably. If the pieces are small they will melt faster and better, reducing the need to break them down or stir too much to smoothen the ganache, thereby reducing the air bubbles.
Procedure: On low heat, in a heavy bottomed saucepan bring the cream and butter to a boil. You will see bubbles here and there. Take care not to burn the cream. Pour it on the chocolate, stir slowly. If u stir vigorously, this creates air bubbles, making the ganache grainy. Let sit for 3-4 minutes or until the chocolate melts completely. Use a spatula to stir briefly to combine. Add extracts if using. It will be quite fluid at this stage and will continue to thicken as it stands. Wrap the bowl with cling film and allow to cool. Use as needed.
Problems you may have with ganache: In case you run into trouble with this delicious thing...
Grainy ganache: If you whisk too much, your ganache may turn out grainy. If this happens, no catastrophe, strain it with a fine metal strainer ( as fine as a tea-strainer). If there still continue to be bubbles, strain multiple times till you get a smooth ganache.. at least a much smoother one! I have managed a fairly smooth ganache, but not an absolutely smooth one so far, sigh!
Lumpy (kick-myself) ganache: If you mess up with the temperature of the ingredients and have a lumpy mass on your hand, then you may try to salvage it by heating in the microwave or a double boiler ( can't really say, but you may be lucky!) and use it as a topping for your kids' ice-cream. Chocolate is chocolate and delicious even if its dull and dreary, it still sells with them and us!
Curdling: God forbid (forgive the exaggeration, but this is a serious matter for us), if your ganache curdles, gently stir in a couple of tablespoons of hot cream (if you happen to have that extra pack of cream) , keeping your whisk or spatula submerged. Then strain, pray for it to work.
Storing: Ganache made with only heavy cream and chocolate (with no added butter and the rest of the things) can be stored at room temp for 2 days, in the refrigerator for a week and frozen for 3 months. If you have added butter, its better to refrigerate the ganache. I find it very handy to have ganache in the freezer for use as cake frosting or as dessert topping . Frozen ganache can be microwaved on HIGH power for a minute or more to get it all gooey and liquid in no time.
Wicked Ways With Ganache : You could use ganache to either pour, whip or pipe it for different kinds of decorative effect.
Pouring ganache : If you want to pour ganache on a cake, first brush any crumbs off the cake. Pour as soon as it is just slightly warm but still pourable. If pouring ganache on a chilled dessert like a mousse, chill the mousse thoroughly so that the warm ganche does not melt your dessert. It will also set quickly. If you would be pouring the ganache on a cake, you could place the cake on a cooling rack with a tray underneath to catch the drip and pour the ganache. Then lift the cake carefully ( with heart in mouth) and place on the cake platter. I prefer to keep it on the serving platter, then pour the ganache in the center. Tilt the platter very very carefully to spread the ganache, no need to use a spatula. I did this for the Queen Of Sheba Cake cake below and was very pleased with the results. I read about this trick somewhere, not able to recall the source.
Whipped ganache: This is ganache made airy, is lighter in color. Dreamy, I so want to try this!! Rose Beranbaum recommends (refer source) using 6 ounces / 168 grams of bittersweet chocolate and 360 ml / 1 1/2 cups /12 ounces of heavy cream. Cool to 65 to 68 °F/20°C. Temperature is important. Beat only until soft floppy peaks form when the beater is lifted. She says, when it starts thickening, it's safest to beat by hand. If you over whip, it becomes grainy.
To whip or pipe ganache the ganache must be cool. Cool it at room temperature or place on a bowl of ice till its cool to the touch but not very cold. Do not whip when its too cold. If the ganache gets very cold, keep it in a warm place in the kitchen to warm, do not reheat. Whipped ganache looks fabulous when piped on a dark ganache frosted cake.
Piping: To pipe, cool the ganache till thick enough to pipe.
Leftover ganache : If you have any left over, you could make truffles or simply freeze for later use. To make truffles, refrigerate ganache till very firm. Scoop out small balls with a melon baller or spoon, then roll in cocoa. Keep refrigerated.
If making ganache for the very first time, you may find this video useful. http://www.joyofbaking.com/
Gulping about the calories here? Check out this recipe for Low Fat Milk Ganache, you can have your cake and eat it too!