1. Combine potatoes, apples, and 1 teaspoon salt in a colander. Let stand 20 minutes, pressing occasionally with the back of a spoon until barely moist. Combine potato mixture, remaining 1/2 teaspoon salt, and pepper in a large bowl. Weigh or lightly spoon flour into a dry measuring cup; level with a knife. Add flour to potato mixture; toss well to combine.
2. Heat a 12-inch nonstick skillet over medium-high heat. Add 1 1/2 tablespoons oil to pan, swirling to coat. Add potato mixture in 1/3-cupfuls to pan to form 4 latkes; flatten slightly. Cook 6 minutes on each side or until golden brown. Remove latkes from pan; keep warm. Repeat procedure 3 more times with remaining oil and potato mixture. Sprinkle latkes evenly with sugar.