Pre-heat oven to 350F / 180C. Grease and flour, spray or line an 8 inch square pan with parchment paper.
Melt the chocolate separately. Let cool to lukewarm.
In the mixing bowl cream the butter and sugar until fluffy, 2-3 minutes, add the eggs one at a time beating well between each addition, add the vanilla. Stir in the flour and salt with a wooden spoon or spatula.
Transfer half the batter to a clean bowl and stir in the melted dark chocolate, in the mixing bowl stir in the white chocolate.
Spread half the dark chocolate batter on the bottom of the prepared pan, drop spoonfulls of the white chocolate batter on top and gently spread as best you can. Spoon the remaining dark chocolate batter on top and swirl with the tip of a knife through the batter and the batter is spread evenly.
Bake for 20-25 minutes or until the sides start to pull away from the pan. Test with a toothpick for doneness, there should be moist crumbs attached. Let cool in the pan on a wire rack. Cut into 16 squares. Enjoy!
Notes
How to store the Marble Brownies?
Keep leftover marble brownies in an airtight container at room temperature for up to 3 days, or in the fridge for up to 5 days. If you like them extra fudgy, let them sit at room temp before serving.To freeze, wrap individual squares in plastic wrap and place in a freezer-safe container or bag. They’ll keep well for up to 2 months. Thaw at room temperature before enjoying.