• Preheat the oven to 350°F(177°C). Grease 8 inch (20cm) square oven-proof dish and line the bottom and sides with parchment paper, about 2 inches(5 cm) of overhang on each side.

Blondie Batter

• Place the flour and salt in a medium bowl and stir. Set aside.
• Put the brown sugar in a medium bowl and pour melted butter. Stir with a whisk until combined well.
• Add the egg and mix until combined. Mix in the vanilla.
• Add the flour in and stir until just combined.  When there is no visible flour, stop stirring. Set aside the bowl.

Cocoa Brownie Batter**

• Place the cocoa powder, flour and salt in a small-medium bowl and stir with a whisk. Set aside.
• Put the granulated sugar in a medium bowl and pour melted butter. Stir until combined well with a whisk.
• Add the egg and whisk until combined. Mix in the vanilla.
• Add the cocoa mixture and stir with a spoon/spatula until just combined. When there is no visible cocoa mixture, stop stirring.

Assembling

• There will be two layers with each batter. So for the first layer, you need to use half of each batter. We will make a check pattern in each layer. Cover ¼ of the baking pan with blondie batter and spoon brownie batter next to it. Then spoon brownie batter next to blondie batter and blondie batter next to brownie batter. For the next layer, place each batter on top of the opposite batter (brownie batter on top of the blondie batter and vice versa). 
• Use the tip of a knife, randomly make gentle swirls by going from one side to other side and from the bottom right to top. Don’t make too many swirls otherwise the brownie batter and blondie batter will be mixed more than needed and there will be too much brownie layer when baked. Instead, use the leftover batter to make a nice design. There’ll be some batter left both in blondie and brownie bowls at least a teaspoon. Take them and place the batter where needed.  For example if there is too much blondie batter seen at the top, place a few drops of brownie batter and use the tip of a knife and make small swirls at the top without going deep.

Baking

• Bake for almost 28 minutes until the top is lightly browned and a toothpick comes out almost clean with a few moist crumbs. Baking time may differ from oven to oven so check it after 25 minutes. Once you remove it from the oven, let it completely cool in the pan before slicing.