Grate potatoes in food processor with coarse shredding blade. Place half the potatoes in sieve over bowl and reserve. Fit steel blade in processor, add onions and pulse with remaining potatoes until all pieces approx 1/8" and look coarsely chopped, 5-6 one sec pulses. Mix with reserved potato shreds in sieve and press against sieve to drain as much liquid into bowl. Let liquid stand until starch settles to bottom (about 1 min)

Pour off liquid leaving starch in bowl. Beat egg then potato mixture and remaining ingred (except oil) into starch.