Preheat the oven to 350°F. Grease and line an 8X8 pan with parchment paper. set aside.
Melt the butter and chocolate in the microwave for 20-second intervals. Until the chocolate starts to melt.
1 cup Butter, 1½ cup Semi-sweet chocolate chips
Once the chocolate is completely smooth, add the cocoa powder and mix. Let this mixture sit for a few minutes. Cocoa powder needs to bloom and activate.
½ cup Cocoa powder
Whisk both sugars. Add the eggs one at a time. Add the yolk and vanilla extract and mix. Add this mixture to the chocolate mixture.
1 cup Granulated sugar, 1 cup Brown Sugar, packed, 2 Eggs, 1 Yolk, 1 tablespoon Vanilla extract
Whisk together the flour, salt, and coffee powder. Add this mixture to the above mixture. DO NOT OVERMIX.
½ teaspoon Salt, 1 cup All-purpose flour, 1 tablespoon Coffee powder
Take ½ cup of this mixture and set it aside. We need this for the marbling effect.
Pour the batter into the prepared pan and smooth out the surface. Set aside.