Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan.

Melt 3 tablespoons of unsalted butter in a medium saucepan over medium heat. Stir in ½ cup of brown sugar and let bubble for 2-3 minutes until thickened. Pour into the cake pan and arrange the sliced apples on top.

In a large bowl, whisk together 1½ cups of flour, 1½ teaspoons of baking powder, ½ teaspoon of baking soda, ½ teaspoon of salt, 1 teaspoon of cinnamon, and ¼ teaspoon of nutmeg.

In another bowl, cream together ½ cup of softened butter and ¼ cup of sugar until fluffy. Add 2 eggs and 1 teaspoon of vanilla. Mix in ½ cup of sour cream and ¼ cup of milk until smooth.

Gently fold the dry ingredients into the wet ingredients until just combined. Do not overmix.

Spread the batter evenly over the apples and caramel in the pan.

Bake in the preheated oven for 40-45 minutes until golden brown and a toothpick comes out clean.

Let the cake cool in the pan for 10-15 minutes, then invert onto a serving plate.

Slice and serve warm, optionally with vanilla ice cream or whipped cream.