01 - Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper, allowing extra for easy lifting.
02 - Whisk flour, baking powder, and salt together in a medium bowl until evenly blended.
03 - Beat butter, brown sugar, and granulated sugar with an electric mixer until pale and creamy, about 2–3 minutes.
04 - Mix in the egg and vanilla extract until fully integrated into the creamed mixture.
05 - Gradually blend dry mixture into the wet ingredients, mixing just until combined. Do not overmix.
06 - Reserve 1 cup of dough for the crumble. Press remaining dough firmly into an even layer in the prepared pan.
07 - Toss diced apples with sugar, lemon juice, cinnamon, and nutmeg in a separate bowl.
08 - Evenly distribute apple mixture over the cookie base.
09 - Combine caramel candies and heavy cream in a microwave-safe bowl. Heat in 20-second intervals, stirring until smooth. Drizzle caramel over the apples.
10 - Sprinkle reserved dough evenly over the caramel and apple layers.
11 - Bake for 40–45 minutes until the top is golden and caramel is bubbling.
12 - Allow bars to cool completely in the pan. Lift out using parchment and slice into 16 bars.