In your first bowl, beat your cream into soft peaks. Sprinkle in your powdered sugar and matcha. Freeze until firm.
In your second bowl, sift together your matcha, sweet rice flour, sugar, and salt. Slowly whisk in your cold water.
Cover with plastic and steam for about 3 minutes. Using a spoon/spatula, beat and stretch this dough until it becomes elastic.
Dust your work surface and begin "rolling" our your dough. Cut into squares and set aside.
Work quickly and fill each square with your firm ice cream. Pinch to seal and keep in your freezer.
It helps to scoop out miniature balls out of your set ice cream and allowing them to firm up as well. Laying your cut mochi in muffin tins for ease also helps. Remember to work rather quickly and with later consideration, I actually found that working with the mochi sheets while they were still slightly warm was easier.
Recipe by The Squishy Monster at http://www.thesquishymonster.com/2013/02/green-tea-mochi-ice-cream.html