Beat egg whites at medium speed with an electric mixer until stiff peaks form.
Whisk egg yolks until thickened. Stir in potato and next 4 ingredients. Fold in egg whites.
Pour oil to depth of 1/2 inch in a large heavy skillet; heat to 350°. Drop potato mixture by teaspoonfuls into hot oil; fry, in batches, 1 to 2 minutes on each side or until golden. Drain on paper towels. Serve immediately with sour cream and caviar.