01 -
Preheat oven to 350°F. Grease and flour a 9x13-inch baking dish or line with parchment paper, ensuring corners are well covered.
02 -
Whisk together flour, sugar, and salt in a large bowl; set aside.
03 -
In a medium saucepan over medium heat, combine butter, cocoa powder, and Coca-Cola. Stir constantly until melted and mixture reaches a gentle boil.
04 -
Immediately pour hot cocoa-Cola mixture over dry ingredients. Stir gently until just combined, ensuring no dry pockets remain.
05 -
Stir in eggs, buttermilk, baking soda, and vanilla extract until batter is smooth. Fold in marshmallows if using.
06 -
Pour batter into prepared pan and spread evenly. Bake 30-35 minutes, or until a toothpick inserted in the center comes out clean.
07 -
While cake bakes, melt butter in medium saucepan over medium heat. Stir in Coca-Cola and cocoa powder, bring to a boil while stirring constantly.
08 -
Remove from heat and whisk in sifted powdered sugar gradually until smooth and spreadable. Stir in vanilla extract.
09 -
Pour warm frosting evenly over hot cake. Use offset spatula or spoon to spread to edges. Frosting will slightly soak in as it sets.
10 -
Allow cake to cool at room temperature before slicing. Serve warm or at room temperature for best texture.