36 whole walnuts, shelled
4 pounds of green or purple seedless grapes
1 tablespoon of potato starch dissolved in 1 tablespoon of cold water
1. String the walnuts in the following manner: Tie a knot one inch from the ends of the two strings each 12 inches long. Then thread the end of one string through the eye of a strong needle. As if you were stringing beads, insert the needle through the center of 18 walnuts. Tie a knot after the last walnut and join the unstrung end of the string into a loop. Thread the second string and loop the other walnuts similarly.
2. A cup at a time, purée the grapes in an electric blender for about 10 seconds high speed, or until they liquefy. Strain the blend through cheese-cloth-lined sieve set over a 2-quart saucepan and discard the skins.
3. Bring the blended purée to a boil over high heat, stirring occasionally. Boil briskly, uncovered, for about 15 to 20 minutes, or until the blend has cooked down to two cups. Stir in the potato starch-water mixture and stirring constantly, cook another minute or two, until the sauce thickens enough to coat a spoon heavily. Set aside.
4. Holding the looped end, dip the strings of walnuts into the sauce, coating them thoroughly. Hang the loops outdoors where they will quickly dry. Place a paper plate under the strings to catch the drippings. If you have a fan then you can dry them even quicker indoors. When the nuts have dried and are no longer sticky to the touch, warm the juice to lukewarm and dip the walnuts again. Dry as before, then repeat the dipping and drying process two or three more times, until the nuts are completely coated and there is not longer any separation between them.