Step 1: Preparation Preheat your oven to 350°F (175°C). Grease an 8×8 or 9×9 inch baking pan thoroughly with butter or non-stick spray. For even easier removal, line the pan with parchment paper, leaving an overhang on the sides to lift the blondies out later.
Step 2: Mixing the Base In a large mixing bowl, whisk together the melted butter, brown sugar, and granulated sugar until the mixture is smooth and well combined. Add the eggs and vanilla extract, whisking again until the batter looks glossy.
Step 3: Adding Dry Ingredients Gently stir in the all-purpose flour, baking powder, salt, and cinnamon. Use a spatula to fold the ingredients together just until no streaks of flour remain. Be careful not to overmix, as this can make the blondies tough.
Step 4: Incorporating the Fruit Peel and dice your Granny Smith apples into small, uniform pieces (about half an inch). Gently fold the diced apples into the blondie batter until they are evenly distributed.
Step 5: Layering with Caramel Spread about half of the batter into the prepared baking pan. Drizzle the 1/2 cup of caramel sauce evenly over the bottom layer. Spoon the remaining batter over the caramel, using a knife or spatula to gently spread it to the edges. It is okay if some caramel peaks through.
Step 6: Baking and Cooling Place the pan in the center of the oven and bake for 35 to 40 minutes. The top should be golden brown and a toothpick inserted into the center should come out with just a few moist crumbs. Let the blondies cool completely in the pan before slicing into squares.