#### **Step 1: Caramelize the Apples**
In a **10-inch nonstick skillet**, melt **butter over medium heat**. Stir in **brown sugar and cinnamon**, then add the **apple slices** in an even layer. Cook for **3-4 minutes**, until the apples are tender and coated in caramel. Remove from heat.
#### **Step 2: Prepare the Batter**
In a bowl, whisk together **flour, baking powder, salt, cinnamon, and sugar**. In another bowl, beat **egg, milk, vanilla, and melted butter**. Gradually stir the wet ingredients into the dry ingredients until smooth.
#### **Step 3: Assemble & Cook the Cake**
Pour the cake batter evenly over the caramelized apples. Cover with a lid and cook on **low heat for 15-20 minutes**, or until the center is set and a toothpick inserted comes out clean.
#### **Step 4: Flip & Serve**
Run a spatula around the edges to loosen the cake. Place a large plate over the skillet and carefully **invert the cake onto the plate** so the apples are on top. Serve warm with **whipped cream or ice cream**.