Beat the egg with the yogurt and milk (or just the yogurt, if you're using the plain normal variety) and set aside. Combine the flour, baking powder, baking soda, cinnamon and sugar in a bowl. Peel, quarter and core the apples, then grate them; I use a food processor, but a coarse Microplane or other grater would work easily, I'd imagine.
Pour the yogurt mixture into the flour bowl, tip in the grated apples and fold it together.
Pour enough oil to come about 1/4 inch up in a skillet and put on the stove to heat. Dollop spoonfuls -- I use a round soup spoon -- of the apple batter into the sizzling oil; a rubber spatula (the one you used to fold the batter together) will help you scrape the batter off the spoon and press down on the little latkes in the pan. Don't worry about making perfect round pancakes; I like these a bit raggedy and skew-whiff. Fry for a minute or two, until the latkes are a golden brown on the undersides; you can see from the top as they start firming up underneath. Flip them with 2 metal spatulas and fry for another minute on the uncooked side.
Remove to a tray lined with paper towels to blot the excess oil and continue cooking until you've used up all the batter. Top with maple syrup.