Preheat oven to 350°F (175°C) and grease a 9-inch cast-iron skillet, then place it inside to warm while you prep filling and batter.

Sauté sliced apples with brown sugar and cinnamon in melted butter over medium heat until tender and caramelized, about 8 minutes.

Drizzle fresh lemon juice over the spiced apples, tossing gently to coat and brighten flavors, then transfer the warm filling to a bowl.

Whisk together all-purpose flour, granulated sugar, baking powder, and salt in a mixing bowl until evenly blended.

Pour melted unsalted butter into the dry mix and stir until the texture resembles coarse crumbs.

Gradually pour in milk, stirring gently until a smooth, thick batter forms.

Spread the batter evenly in the warmed skillet, then dollop the apple cinnamon filling on top.

Slide the skillet into the oven and bake at 350°F for about 25 minutes.

Let cool for 5 minutes, then slice into wedges, top with vanilla ice cream or chopped nuts, and enjoy warm.