Grate potatoes and onion with the shredding disk in a food processor. With a towel or cheesecloth squeeze liquid from potato and onion.

Add egg, matzo meal, salt, and pepper to the potato/onion mixture. Mix and set batter aside for 10 minutes.

Place the oil or schmaltz (or a combination of the two) in a large skillet so that when melted there is a depth of 1/4 inch (for a 10-inch skillet you'll need 1 cup of melted oil/schmaltz). Heat over medium-high heat until a piece of the latke mixture sizzles immediately.

Place about ¼ cup batter into the hot oil. Flatten to form a latke. Fry the latkes until golden on both sides. Repeat until the pan is full but the pan is not too crowded.. Cook until deeply golden-brown, 4 to 5 minutes per side, adjusting the heat if necessary.

Drain the latkes. Transfer the latkes to a paper towel-lined baking sheet to drain for 2 minutes.

Serve immediately with applesauce and sour cream, or transfer the latkes to the wire cooling rack set in the baking sheet and keep warm in the oven for up to 30 minutes while you continue cooking the rest of the latkes.