Preheat the oven to 350ºF (180ºC). Grease an 8-inch square cake pan or baking dish or line with parchment paper. (I used a ceramic baking dish.*)
In a medium-sized bowl, whisk together the flour, cinnamon, baking soda, salt and nutmeg until well blended.
In large bowl, beat the butter, granulated sugar and brown sugar together until pale and fluffy. Beat in the egg until incorporated, then beat in the vanilla extract.
Stir in the flour mixture in 2 additions, followed by half of the sour cream after each addition. Mix just until combined. Do not over mix. Fold in the cooled, drained apples.
Transfer the batter to the baking dish. Smooth the top with a spatula. Bake until the cake is golden brown and a toothpick inserted into the center of the cake is clean or has a few moist crumbs attached, about 23-28 minutes. Do not over bake. Let the cake cool in the pan for at least 15 minutes.