Preheat your oven to 350°F (175°C) and prepare an 8-inch square pan with parchment paper and baking spray.

In a saucepan, melt 4 tablespoons of unsalted butter and 1 cup of dark brown sugar over medium heat, stirring until it begins to boil. Add 1 teaspoon of ground cinnamon and pour into the prepared pan.

Slice 3-4 medium apples thinly and arrange them over the caramel base in the pan.

In a mixing bowl, whisk together 1 ½ cups of all-purpose flour, 1 ½ teaspoons of baking powder, 1 teaspoon of cinnamon, and a pinch of salt.

Cream together 1 cup of granulated sugar and ½ cup of softened unsalted butter until light and fluffy, about 3-4 minutes.

Add 2 large eggs one at a time and then stir in 1 teaspoon of vanilla extract.

Gradually alternate adding the dry mixture and ½ cup of whole milk to the creamed butter mixture until just combined.

Pour the cake batter over the arranged apples and caramel in the pan, spreading it evenly.

Bake for 40-50 minutes until golden brown and a toothpick comes out clean.

Allow the cake to cool for about 15 minutes before inverting onto a serving platter.