In a separate medium bowl, whisk together the sugar, vanilla extract, and egg until fluffy, about 1 minute.
Melt the butter and chocolate chips together until smooth.
Stream the melted butter and chocolate into the bowl, whisking constantly until combined.
Fold in the flour, cocoa powder, chopped chocolate, and salt until just combined.
Evenly spread the brownie batter into the pan.
Use a spoon to dollop the reserved blondie batter on top. Then use a toothpick or skewer to swirl them together.
Sprinkle the extra chopped chocolate on top.
Bake for 25-26 minutes or until a toothpick inserted into the center comes out with just the tip smeared in chocolate.
Let them cool completely on a wire rack before cutting, then enjoy!