1. Peel sweet potatoes and grate by hand through a large-hole grater. Put grated sweet potato into slightly iced water and let stand for 10 minutes.
2. Remove any ice that hasn't melted and drain off water from sweet potatoes. Squeeze out any excess water from grated sweet potatoes and transfer to a cutting board. Chop potatoes just a few times and transfer to a mixing bowl.
3. Grate the onion and add to potatoes along with flour, eggs, salt, and pepper. Mix until combined.
4. Heat 1/4 cup oil in a large frying pan until hot (just rippling). Drop rounded tablespoons of potato-onion batter into pan and flatten with the back of the spoon until they are evenly flat and about 1/8 inch thick. Cook until medium to dark brown, turn and brown the other side. Remove pancakes onto paper towels to drain and keep warm in a 200-degree oven until ready to serve.
Serve with applesauce and sour cream.