• CAKE
• In a large mixing bowl, add 2 cups sugar. Then sift the 2 cups flour and 4 tbsp cocoa powder into the bowl. Sifting the flour and cocoa is an important step so don't skip it!
  
• Then add the 1/2 cup butter on top of the sifted ingredients.
  
• Put the 1 cup water and the 2/3 cup vegetable oil in a small saucepan and bring to a boil. Pour all at once over the flour, sugar, and cocoa mixture. 
  
• Stir until well combined.
  
• Add the 2 eggs, 1/2 cup buttermilk, 1 1/2 tsp baking soda, and 1 tsp vanilla and stir until smooth.
  
• Spray the baking dish with cooking spray. Pour into a 9x13 cake pan or large cookie sheet and bake at 350º for 25-30 minutes or until the cake bounces back when touched lightly in the middle. Don't overbake.
  

Frosting

• Put the 1 cup sugar, 1/3 cup milk, and 5 tbsp butter into a saucepan. Bring to a boil. Do not boil for more than 20 seconds. Remove from heat and add the 2 cups milk chocolate chips. Stir until dissolved and then add the 1 tsp vanilla and stir again. If using the marshmallows and/or the chopped nuts, add those in and gently stir. Immediately pour onto the cake and spread. This sets ups fast so work quickly. 
• This is best if made the day ahead. Allow at least 6-8 hours to set up if possible.