Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a medium-sized mixing bowl, melt the unsalted butter until it’s smooth. Allow it to cool until it’s lukewarm to the touch.
Add the packed light brown sugar and granulated sugar to the melted butter. Whisk until the mixture is well combined and creamy.
Crack in the eggs, one at a time, and stir until fully incorporated. Add the vanilla extract and mix well to combine.
In a separate bowl, whisk together the all-purpose flour, baking soda, and fine sea salt. Gradually add this dry mixture to the wet ingredients, stirring until just combined.
Gently fold in the chopped chocolate sandwich cookies, semisweet chocolate chunks, white chocolate chunks, and rainbow sprinkles.
Pour the blondie batter into the prepared baking pan, spreading it evenly. Bake in the preheated oven for 20-25 minutes or until the edges are lightly golden and a toothpick inserted in the center comes out with a few moist crumbs.
Once baked, remove the blondies from the oven and let them cool in the pan for about 10 minutes. Carefully lift them out using the parchment paper overhang and transfer to a wire rack to cool completely. Cut into squares and enjoy!
