Beat the egg with the yogurt and milk and set aside. Combine flour, baking powder, baking soda, cinnamon, and sugar into a bowl. Peel and core the apples, then grate them; I use a food processor, but a coarse grated 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 a skillet and put on the stove to heat. Dollop spoonfuls of the apple batter into the sizzling oil; a rubber spatula will help scrap the batter off the spoon and press down on the latkes in the pan. Don't worry about making perfect round pancakes; fry for a minutes or two, until the latkes are a golden brown on the underside; you can see from the top as they start firming 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.