Using a food processor or cheese grater, grate the potatoes and place in a bowl using a paper towel to remove excess water. Grate the onion in with the potato.
Add egg, salt, and matzo meal to the potato/onion mixture and mix well with a fork. If mixture seems too watery, add more matzo meal.
Heat 2-3 inches of oil over medium-high heat In a deep pan or cast iron skillet. Add a drop of the potato mixture to test the heat of the oil. If it bubbles, it's ready!
Using an ice cream scoop or large soup spoon, drop the potato mixture into the oil being careful not to over crowd the pan. Flatten the pancakes with a metal spatula to ensure even cooking.
After 3-4 minutes, check for color and flip once browned on one side. Flatten again with the spatula and cook until browned on both sides.
Lay cooked latkes on plate or baking sheet lined with paper towel to absorb excess oil.
Continue working in batches until all of the potato mixture is gone. Serve with sour cream, horse radish, or apple sauce.
Notes
Keep potato latkes in oven heated to warm to keep hot until dinner is served.