For the apple topping, toss the sugar, cinnamon, and apples together. Spread this out in the buttered baking pan you'll be using to bake the cake in, and set aside.
In a small bowl, stir the yolks, 1 tbsp of the sour cream, and vanilla extract.
In a large bowl, stir the flour, sugar, baking soda, baking powder, nutmeg and salt. Add butter, the rest of the sour cream, and blend until the dry ingredients clump. Beat on high for 1 1/2 minutes. Add egg mixture and beat well.
Pour the batter in your prepared pan and bake at 350 ºF for 40-45 minutes.
Let cake cool for 10 minutes before carefully flipping the cake onto a serving platter.
Boil apple juice and balsamic vinegar on medium heat for 12 minutes until reduced to a syrup. Brush evenly over cake, serve, and enjoy!