Preheat your oven to 325-F. Line the bottom of a springform pan with parchment paper and spray the sides with nonstick cooking spray.
Peel, core, and cut the apples into 1/3-inch thick slices. Set them aside.
Melt 1/2 cup of the butter and add it to the bowl of a stand mixer (or use a hand-mixer). Add 1 cup white granulated sugar and mix well. Add 2 eggs, one at a time, mixing in between.
Mix the flour, baking powder, and salt in a separate bowl until combined.
Add the flour mixture to the butter-sugar-eggs mixture and mix until combined.
Transfer the batter to the prepared springform pan and press the apples into the batter in the shape of a ring. The apples should be seated in the batter but not fully covered. The top bit of the apple can stick out. They should be close but not quite touching. Add a second ring inside the first until the batter is filled with apples.
Dust the apples with 1 teaspoon of cinnamon and bake at 325-F for about 50 minutes.
Melt the remaining 1/4 cup of butter and transfer it to another bowl. Add the remaining 1/2 cup of sugar and mix until well-combined. Mix in the last 2 eggs one at a time until blended.
Remove the cake from the oven and pour the topping over the cinnamon-dusted apples. Return the cake to a 350-F oven for about 30 minutes or until cooked through.
Dust with cinnamon sugar and serve - ½ teaspoon mixed with 2 tablespoons of powdered sugar. Slice and serve!