Peanut oil, for frying
Sour cream or crème fraîche, to serve
Applesauce, to serve
FILL a medium bowl with ice water.
GRATE the baking potatoes and sweet potato using the medium holes on a box grater. Add the grated potatoes to the ice water and set aside.
USE the fine holes on the grater to grate the onion or shallot.
DRAIN the potatoes very well, squeezing out as much water as possible. In large bowl, combine the potatoes with the onion. Squeeze again to remove as much moisture as possible. To do this, grab the mixture a handful at a time and squeeze over the sink, then transfer to a dry bowl. When all of the mixture has been squeezed, add the eggs, flour and a bit of salt (start with 1/2 teaspoon), then mix well. Set aside.
HEAT about 1/4 inch of peanut oil to 360° in a large, deep sauté pan over medium-high. To test the oil, drop a pinch of flour into the mixture. If the oil is ready, the flour should sizzle and brown almost immediately.
SET a wire rack over a rimmed baking sheet. Heat the oven to 350°.
WORK in batches, using about 2 to 3 tablespoons of the potato mixture per pancake, drop the batter into the oil. Do not crowd the pan. Flatten each with a spatula and fry for 4 minutes per side, or until golden and crisp. As you fry the batches, you may need to add oil to the pan. Be sure to let it return to temperature between batches and additions of oil.
TRANSFER the pancakes to a wire rack as they finish. Once all of the pancakes are fried, place them (rack and baking sheet) in the oven and heat for 5 to 10 minutes, or until warmed through. The pancakes also can be prepped in advance up to the oven stage, then reheated just before serving.
TO SERVE, sprinkle lightly with salt and accompany with sour cream and applesauce.
Nutrition information: Per pancake: 90 calories, 30 calories from fat (33 percent of total calories), 3.5 grams fat (0.5 grams saturated, 0 grams trans fats), 20 milligrams cholesterol, 12 grams carbohydrate, 1 grams fiber, 1 gram sugar, 2 grams protein, 70 milligrams sodium.