Make brownie batter: Whisk butter and both sugars together
Whisk in the eggs and vanilla extract
Whisk in the flour, salt, and cocoa powder then set aside
Make the blondie batter: Mix butter and sugars together
Whisk in the egg and vanilla extract
Add in flour and salt
Alternate pouring brownie batter, then blondie batter into the pan
Continue pouring each one on top of the other
Swirl the top with a knife then bake at 350°F for 25-35 minutes
Let cool then slice!
Get the recipe!