Peel, core, and finely dice the apples. Pat them dry with a paper towel to remove any excess moisture
Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal
In a large bowl, whisk together the melted butter and brown sugar until smooth and well combined. Add the eggs and vanilla extract and whisk until fully incorporated
In a separate bowl, whisk together the flour, cornstarch, and baking powder
Add the dry ingredients to the wet ingredients, mixing just until combined. Avoid overmixing
Gently fold in the diced apples and white chocolate chips until evenly distributed throughout the batter.
Spread the batter evenly into the prepared baking pan
Drizzle ¼ cup of caramel sauce over the top of the batter. Use a knife or toothpick to gently swirl the caramel into the batter
Bake for about 30 minutes, or until the edges are golden brown and the center is set but still slightly soft
Allow the blondies to cool in the pan for at least 1 hour before slicing. They will continue to set as they cool
Cut into 12 bars, then drizzle with the remaining caramel sauce and sprinkle with flaky sea salt