Ingredients

The following ingredients have 4 Servings
  • 1 cup unsalted butter ((226g), cut into pieces)
  • 1 cup water ((235ml))
  • ⅓ cup cocoa powder ((35g))
  • 2 cups all-purpose flour ((250g))
  • 1 ½ cups granulated sugar ((300g))
  • ½ cup light brown sugar (firmly packed (100g))
  • 1 teaspoon baking soda
  • ¾ teaspoon salt
  • ½ teaspoon instant coffee optional
  • ½ cup sour cream ((125g))
  • 2 large eggs room temperature (lightly beaten)
  • 1 teaspoon vanilla extract
  • ½ cup whole milk ((118ml))
  • 11 Tablespoons unsalted butter
  • ¼ teaspoon salt
  • ½ cup cocoa powder ((50g))
  • 5 cups powdered sugar ((600g))
  • 1 teaspoon vanilla extract
  • 5 cups mini marshmallows (one 10 oz bag (283g))

Instruction

  • Preheat your oven to 350F/175C and lightly grease and flour a 10x15 jelly roll pan (or spray with baking spray).
  • In a medium-sized saucepan, combine butter, water, and cocoa powder. Turn heat to medium low and stir occasionally until butter is melted.
  • Increase heat to medium-high and (stirring frequently) bring to a rolling boil. Remove from heat and allow to cool for 15-20 minutes.
  • Meanwhile, whisk together flour, sugar, baking soda, salt, and instant coffee (if using) in a large bowl. Make a well in the center and add sour cream, eggs, and vanilla extract. Whisk together sour cream/eggs/vanilla in the well, then use a spatula to combine all ingredients in the bowl (mixture will be thick).
  • Add slightly cooled chocolate mixture to the flour mixture and stir until well-combined (be careful, chocolate mixture will still be a bit hot).
  • Pour batter into prepared pan and carefully (don’t spill!) transfer to 350F (175C) oven. Bake for 20-25 minutes or until toothpick inserted in center comes out clean or with a few moist crumbs, but while cake is baking measure out your marshmallows and prepare frosting.