Preheat the oven to 350 degrees F and line a 9x9 inch square pan with parchment paper.

In a large bowl, add the brown sugar, granulated sugar, chocolate, and butter. Heat the mixture in the microwave in 20 second increments until everything is fully melted. Whisk the mixture until smooth.

Add the eggs and vanilla to the butter, sugar, chocolate mixture, and whisk until fully combined.

Next, fold in the flour, cocoa powder, and salt until just combined.

Lastly, fold in the chopped chocolate.

Set aside as you make the blondie layer.

In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

In a separate bowl, mix together the melted butter and brown sugar until fully combined.

Then, mix in the egg and vanilla.

Fold the dry ingredients into the wet until just combined.

Lastly, fold in the chopped chocolate.

In the prepared square pan, add about ⅔ of the brownie batter and smooth into an even layer. I reserved about 200g of batter for the top.

Next, add all of the blondie batter in large dollops on top of the brownie layer.

Fill in the gaps between the blondie batter with the remaining brownie batter.

Lastly, top the brownie blondies with more chopped chocolate, if desired.

Bake for about 30 minutes or until the blondie layer is golden and the brownie layer appears set.

Allow the brownie blondies to cool completely in the pan before removing.

Cut into diamonds or squares, top with flaky sea salt, and enjoy!