Combine first 4 ingredients in a small bowl, stirring well. Cover and chill until ready to serve.
Combine potato and onion in a colander. Drain 30 minutes, pressing occasionally with the back of a spoon until barely moist. Combine potato mixture, flour, and next 5 ingredients (through salt) in a large bowl; toss well.
Heat a large skillet over medium-high heat. Add 2 tablespoons oil to pan; swirl to coat. Spoon 1/4 cup potato mixture loosely into a dry measuring cup. Pour mixture into pan; flatten slightly. Repeat the procedure 5 times to form 6 latkes. Sauté 3 1/2 minutes on each side or until golden brown and thoroughly cooked. Remove latkes from pan; keep warm. Repeat procedure with remaining 2 tablespoons oil and potato mixture to yield 12 latkes total. Serve with sour cream mixture.