• Preheat the oven to 350°F and line a 9-inch square baking pan with parchment paper.

Prepare the Chocolate Brownie Batter

• Melt the butter then stir in the sugar.
• Whisk in vanilla and eggs until smooth.
• Sift in the flour and cocoa powder and add the salt, mixing just until combined.

Prepare the White Chocolate Batter

• Melt the butter and white chocolate together until smooth.
• Let it cool for a few minutes, then, whisk in the eggs, vanilla and sugar.
• Stir in the salt and flour until just combined.

Bake the Brownies

• Add alternating dollops of each batter into your prepared pan.
• Gently swirl the batters together using a knife or skewer, stopping when you have visible streaks of each.
• Bake for 35 to 40 minutes, or until the center is set. Check by inserting a toothpick into the center. If it comes out with a few moist crumbs, the brownies are done.
• Cool the brownies completely before slicing so you get defined swirls and clean edges.