Preheat oven to 350°F. Line an 8x8 baking pan with parchment paper. Set aside.
In a large mixing bowl, combine butter, brown sugar, granulated sugar, eggs and vanilla extract. Beat with an electric mixture until smooth and fluffy.
Add the flour, baking soda and salt and beat until just combined.
Fold in ¾ of the chopped oreo pieces.
Pour batter into prepared baking pan, speading evenly. Smooth the top with a spatula, then sprinkle the remaining oreo pieces on over the batter.
Transfer baking pan to the preheated oven and bake for 40 minutes or until the edges are golden brown. It's normal that the center of the blondie is slightly underdone in the center.
Once baked, cool blondie for minimum 1 hour.
Once the blondie has completely cooled, fill a large pot half way with water and place over medium heat. Bring water to a simmer. Place a heat-safe bowl over the pot, making sure the bottom of the bowl doesn't touch the water. Add the chocolate chips to the bowl and stir. Stir the chocolate quickly until it's smooth and fully incorporated.
Remove melted chocolate from heat. Using a spoon, drizzle chocolate over the blondie. Allow chocolate to set before cutting.
Cut into 9 pieces. Serve and enjoy!