– Boxed white cake mix – Cocoa powder – Unsalted butter – Coca-Cola – Buttermilk – Eggs – Vanilla extract – Mini marshmallows – Powdered sugar – Chopped pecans
To make the cake batter, combine cake mix, cocoa powder, melted butter, cola, buttermilk, eggs, and vanilla in a large bowl. Mix at low speed for 1 minute, then scrape the sides with a spatula. Increase the mixer speed to medium and beat for an additional 2 minutes until the batter is well blended.
Bake the cake until cooked. Prepare the chocolate icing by melting butter in a saucepan over low heat. Stir in cocoa powder and cola, letting it come to a boil while stirring constantly.
Remove from heat and mix in confectioners' sugar until the frosting is smooth, then fold in pecans if desired. Pour the frosting over the cake and spread it to the edges with a spatula. Allow the cake to cool for 20 minutes before serving.