Peel potatoes and coarsely grate by hand on the largest setting of a box grater, transferring to a large bowl of cold water as you grate. Place the onion in the freezer while you grate the potatoes.
Place a medium bowl under a fine mesh sieve and place the potatoes in the sieve. Use a large wooden spoon or spatula to press out as much of the moisture as possible. Transfer potatoes to a large bowl.
Grate the onion and add to the potatoes. Add the egg, pumpkin, salt and pepper and mix well.
Heat the oil in a 12-inch nonstick skillet over high heat until shimmering, but not smoking. Working in batches, spoon ¼ cup potato mixture per latke into skillet, squeezing out any additional liquid before adding to pan. Flatten the tops slightly with a spatula. Reduce heat to medium-high and cook until the bottoms are browned, about 5 minutes. Turn latkes over and cook about 4 minutes more. Transfer latkes to a paper towel-lined plate to drain. Continue cooking latkes until all of the mixture is gone.
Serve while hot with plain Greek yogurt and applesauce
Makes 8 latkes.