Place the ¼ cup butter in the bottom of an 8 inch cake pan and pop it in the preheating oven until fully melted.
While butter is melting, add the 1 ¼ cup all-purpose flour, 1 ½ teaspoons baking powder, and ¼ teaspoon salt to a medium bowl. Whisk until combined and set aside.
In a large mixing bowl, beat the ½ cup butter and 1 cup granulated sugar together with a hand mixer on medium speed until light and fluffy
Add 1 teaspoon vanilla extract and 2 large eggs. Beat until well combined and scrape down the sides of the bowl.
Beat in the ½ cup whole milk just until combined.
Add in the dry ingredients and beat just until combined. Scrape down the sides of the bowl and mix in any remnants.
Remove the cake pan from the oven.
Add the ½ cup light brown sugar and 1 teaspoon ground cinnamon into the pan of melted butter and stir until combined. Spread the mixture out evenly into the bottom of the pan.
Lay the 2 cups sliced apples on top of the brown sugar mixture.
Spoon the cake batter on top of apple mixture and gently spread until evenly distributed.
Place in the oven and bake in center of oven for 45 minutes or until a toothpick inserted in center comes out clean or with moist crumbs.
Remove the cake from the oven and let cool 10 minutes. Loosen the cake from sides of pan with a butterknife and turn out onto a cake plate.
Let cool before slicing and serving.
Notes
Storage: Place in an airtight container at room temperature for 1 day or in the fridge for up to 4 days. Freezing: Place the cake in a freezer-safe container and store in the freezer for up to 3 months. Thaw in the fridge overnight before serving.