Heat cream in a heavy-bottomed saucepan until almost boiling; pour this over the grated chocolate. Let stand a minute before stirring until smooth.
Cool at room temperature and chill in the refrigerator for at least 4 hours or firm.
Form into small balls about a 1-1/2 teaspoon each and arrange in pachment-lined tray and chill again until firm. note: This truffle recipe will make more than what you need to fill the mochi, but that would not be a problem, wouldn't it ;)
Put glutinous rice in a big bowl. Combine milk, sugar and coffee powder in a bowl or measuring cup, pour over glutinuous rice and mix until smooth- make sure it’s completely free of lumps.
Cover with cling wrap and put inside the steamer. Steam for about 20 minutes. Dust potato flour on clean work surface; hands with some potato starch too.
Remove the hot mochi from the bowl to the pan onto the dusted surface. Divide the mochi into 10-12 pieces by hands.
Let the mochi cool completely before putting filling on so the truffles will not melt but cover the mochi with plastic wrap to prevent it from drying.
When mochi is ready to use, flatten each piece and put one chocolate truffle in the center, and wrap filling by stretching mochi and form each into a ball and round the daifuku.
Repeat the processwith the remaining pieces. If not serving immediately, keep chocolate truffle daifuku in the fridge, covered. Serve with tea or coffee. Enjoy! :)