For the first step, you must preheat the oven to 350 °F then line a 9x9-inch square baking dish or pan with a piece of parchment paper.
In a large bowl, combine butter and 1 ½ cups of brown sugar. Whisk until smooth and lightly fluffy.
Add in your wet ingredients, the eggs and vanilla extract. Continue to whisk until smooth and combined.
Get your dry ingredients, the flour, baking powder, cinnamon, and salt. Gently fold until the batter and smooth and make sure to not overmix.
Toss your chopped apples with remaining brown sugar in a small bowl. Gently fold the juicy apples and the white chocolate chips, if using, into the flour mixture.
Transfer the blondie batter into the prepared baking pan and place in the oven to bake. Bake until the top is lightly browned and a toothpick inserted into the center of the pan comes out mostly clean. Do this for around 30-40 minutes. The blondies will set as they cool down.
Allow the blondies to cool to room temperature before slicing and serving. Enjoy!