Combine diced apples with 2 tablespoons brown sugar, cinnamon, nutmeg, and lemon juice in a small saucepan. Cook over medium heat for 5-7 minutes until the apples soften slightly but still hold their shape, then remove from heat and set aside.

Preheat your oven to 350°F (175°C) and line a 9x13 inch baking pan with parchment paper, then lightly spray. In a large bowl, cream together the melted butter, granulated sugar, and ½ cup brown sugar until smooth. Beat in the eggs one at a time, then stir in the vanilla extract. In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet, mixing until just combined without overmixing.

Spread about two-thirds of the blondie batter evenly into the prepared pan. Spoon the prepared apple mixture over the batter, then drop small spoonfuls of the remaining blondie batter over the apples. Use a knife or skewer to gently swirl the apple mixture and top batter together. Bake for 25-30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with moist crumbs.

Let the blondies cool in the pan on a wire rack. Once cooled (or slightly warm), generously drizzle the pre-made caramel sauce over the top.