Grease and line a square 8 x 8 baking pan with parchment paper.
Use a cookie scooper or a spoon to scoop roughly 1-2 tablespoons of brownie batter into each corner of the baking pan.
Then, use a different spoon or scooper to scoop 1-2 tablespoons of blondie batter into the spaces between the brownie batter, plus one in the center.
Repeat this process by adding brownie batter around the center spot, then adding blondie batter around those spots.
Fill in any remaining spots as you choose, it is fine for it to look haphazard.
Once all of the batter is used and the spots are filled, tap the baking pan on a flat surface and/or gently shake to make sure the batter is filling the entire pan.
Next, take a clean butter knife or a chopstick and draw a zig-zag or "S" shape through the batters.
Place in the oven and bake at 375ºF for 25-30 minutes, until a fork can be inserted and come out clean.
Allow brownie blondies to cool completely before cutting.