Place the potatoes into a colander. Rinse with cold water. Blot dry with paper towels.
Stir the potatoes, 1/2 cup onions, flour and 1/2 cup soup in a medium bowl.
Heat the oil in a 12-inch nonstick skillet over medium-high heat. For each latke, drop 2 tablespoons potato mixture in the skillet, flattening into a 3-inch round with the back of a spoon. Cook the latkes, 5 or 6 at a time, until well browned on both sides. Drain the latkes on paper towels.
Stir the sour cream, remaining soup and onions in a small bowl. Serve the sour cream mixture with the latkes.