Topping
In a saucepan, melt unsalted butter and brown sugar over medium heat. Stir every few seconds until the butter is melted and the mixture thickens (about 1 minute).
Remove the mixture from the heat and stir in ground cinnamon and vanilla. Pour it into a 2x9 cake pan or pie dish (no need to grease).
Layer apple slices evenly on top and overlap if necessary. Refrigerate for 2-3 minutes while we whip up the batter.
Cake Batter
Dry ingredients: Whisk baking powder, flour, nutmeg, cinnamon, and salt in a separate bowl.
Wet ingredients: Use your hand or electric mixer to beat in the ingredients at high speed in this order: butter (1 minute), both sugar types (1 minute), eggs, and vanilla (1 to 2 minutes) until creamy. Scrape the bowl's sides and bottom with your spatula.
Gradually add our dry ingredients to the wet while mixing on low speed, pouring in some milk as you go. Don't overmix. Use your hands to whisk them all if you can.
Baking
Take your topping out of the fridge and pour the warm cake batter over it.
Bake it for about 40 to 50 minutes, but halfway through, cover it with foil to keep the top surface from getting too brown too soon. You'll know it's ready when a small toothpick poked into the middle comes out clean (a few crumbs are fine).
Let it cool on the wire rack for 15 minutes, then flip it onto a plate or cake stand.
You can dig in while it's still warm. But I recommend letting it cool entirely at room temp before slicing. Enjoy.
- To prevent the apples from browning too quickly before baking, toss them in a mixture of lemon juice and water.
- Cast iron skillets are popular for upside-down cakes because they distribute heat evenly and can be inverted easily. But whichever pan you use, ensure it's oven-safe and leakproof, as the caramel sauce can bubble up during baking.
Calories: 534kcal | Carbohydrates: 89g | Protein: 7g | Fat: 18g | Saturated Fat: 11g | Cholesterol: 104mg | Sodium: 613mg | Potassium: 219mg | Fiber: 4g | Sugar: 53g | Calcium: 115mg | Iron: 3mg