Preheat oven to 325 degrees. Place 2 large cookie sheets in oven to heat. Shred potatoes and onion in a food processor. Transfer contents of work bowl to a large bowl. Insert steel blade in processor. Return potato-onion mixture to work bowl and process until finely chopped. Set large strainer over medium bowl. Place potato and onion mixture in strainer and press firmly to extract liquids; reserve liquids.

Return potato mixture to large bowl. Mix in matzo meal, egg yolks, 2 tb chives, salt and pepper. Pour clear portion off reserved potato liquids, leaving thick paste at bottom of bowl. Add paste to potato batter. Beat egg whites until stiff but not dry; fold into batter.

Heat one third cup oil in each of 2 heavy large skillets over medium-high heat. Drop 1 heaping tablespoon potato batter per pancake into hot oil; spread each to 8 cm diameter. Cook pancakes until bottoms are brown, about 4 minutes. Turn and cook until second sides are brown, about 3 minutes. Transfer pancakes to cookie sheets in oven. Repeat with remaining batter, adding more oil to skillet as necessary.

Overlap pancakes on plates. Garnish with smoked salmon and caviar. Sprinkle with chives and serve.