Preheat your oven to 350°F (175°C).

In a 9-inch cake pan, melt ¼ cup of unsalted butter and sprinkle ½ cup of brown sugar over it.

Slice apples into ¼-inch half circles and arrange them in concentric circles over the brown sugar mixture in the pan.

Whisk together 1 ½ cups of all-purpose flour, ¾ cup of sugar, 2 teaspoons of baking powder, 1 teaspoon of cinnamon, and ½ teaspoon of salt.

In another bowl, combine ¾ cup of milk, ¼ cup melted butter, 1 teaspoon vanilla, and 1 egg; mix well.

Pour the wet mixture into the dry ingredients and mix gently until just combined.

Carefully pour the batter over the arranged apples in the pan, smoothing the top.

Bake in the oven for 30-35 minutes until a toothpick comes out clean.

Let the cake cool in the pan for 10-15 minutes before inverting onto a serving plate.