The basic recipe is an adaptation of Philly fudge, i.e., mix some melted chocolate with some cream cheese, and add flavorings. The original truffle recipe was posted at b.org by beathen (Spike's Bitches 20, #2153)
1 lb. candy coating
24 oz. chocolate chips
8 oz. cream cheese - softened
3 tablespoons instant granulated coffee
2 teaspoons water
Dissolve instant coffee in water. Melt the chocolate chips in the microwave, stove or in a double boiler. Mix together the melted chocolate, cream cheese and dissolved coffee until smooth. Let it cool. When it is cool enough to handle, make 1-inch balls and place on wax paper (I put them on wax paper on a cookie sheet). Put the chocolate in the fridge to cool until solid. Heat the candy coating. Coat the cold chocolate balls and let cool.
It makes between 4-6 dozen truffles depending on the size. I usually keep them in the fridge to keep them fresh and so they don't get too soft.
One note here about the order of addition. Mix (I use an electric mixer) the melted chocolate and cream cheese together before adding any liquid flavorings to reduce the possibility of the chocolate seizing. More on this below.
The recipe above makes a boatload of truffles. This year I decided to make smaller batches of several different flavors based on the recipe. The basic recipe I used for the center variations was:
12 oz. chocolate chips (1 standard bag)
4 oz. cream cheese - softened (½ standard package)
flavoring, as needed
Deep chocolate centers - I used a bag of 60% cocoa chips and 1 tsp of vanilla. I melted the chocolate in a double boiler, and it seemed to melt better than the rest of the batches I did in the microwave. The problem with this batch was that I added the vanilla directly to the melted chocolate, and it seized, i.e., the cocoa butter separated from the cocoa solids, very unappetizing. Mixing in the cream cheese did nothing to help. I let it sit in the fridge over night, then carefully remelted the whole mess in the microwave, and mixed it thoroughly with an electric mixer. This did the trick, and I was able to proceed as normal. (I'm not sure if melting the chocolate over the double boiler contributed to the seizing, or if it was just the water in the vanilla, but I didn't have the problem when I melted the chocolate in the microwave.)
Mint centers - I used a bag of white chocolate chips, melted in the microwave. This made for a very smooth base when mixed with the cream cheese. I split this into two parts, roughly one third to two thirds. To the smaller portion I added about ½ tsp of peppermint extract (I did this to taste, so YPEMV). I pressed the mixture into the bottom of a small square container lined with wax paper, and when it had set, I turned it out, and cut the mix into squares with a pizza cutter before coating it.
Coconut centers - To the rest of the white chocolate base made above, I mixed in a ½ cup of shredded coconut that I'd whirled about in a food processor to chop the shreds even finer. These turned out very creamy. I probably could've used an even higher ratio of coconut to base.