Core apples, making a 3/4"-wide cavity, stopping 1/2" from the bottom. Peel top inch of apples and fill with cherries and walnuts. Arrange in an 8" square baking dish.
Drizzle maple syrup over apples and top each with 1/2 tablespoons butter.
Bake, basting occasionally, until apples are tender (45-60 minutes).
Transfer apples to a plate. Pour the liquid fro the baking dish into a bowl; whisk in sour cream. Drizzle over apples and sprinkle with crushed gingersnaps.