You will need some scrap fabric and some rice. Cut two squares out of the fabric (you could use any shape) sized according to the size hands you are warming.
Sew a straight stitch all the way around the edge leaving about an inch or so opening. Snip the corners to make it easier to keep them pointy.
Turn inside out and use a funnel to fill with rice. Add enough rice to make it squishy but not stiff (like a bean bag). Handsew the opening closed. Zap 'em in the microwave for 30 seconds to 1 minute and toast those fingers! Here is my really cute model testing them out.
Until next craft attack,