1/4cupchopped pecanstoast the pecans for more flavor
To make the cake:
Preheat oven to 350 F and lightly grease a 9 x 13 baking dish.
Melt butter in a pan over medium heat. Add the cocoa powder followed by the boiling water, then turn off the heat and set the pan aside.
Mix the flour, sugar and salt in a large mixing bowl to combine. In a separate bowl, beat the buttermilk with the eggs, baking soda and vanilla.
Add the chocolate mixture to the bowl with the flour. Stir a couple of times, then add the buttermilk mixture to the bowl. Stir until well combined. Pour the batter into the prepared pan and bake for 25-30 minutes or until cake is set and a toothpick inserted into the middle comes out clean.
Remove the cake from the oven and sprinkle the mini marshmallows over the top. Turn on the broiler, then put the cake back in the oven for 1 minute or until the marshmallows begin to brown. Watch closely, some broilers work fast! Let cool while you make the frosting.
To make the frosting
Heat a saucepan over medium heat and add the butter. When butter is melted fully, add the cocoa powder and milk and whisk well to combine. Gradually add the powdered sugar in batches, whisking well between each batch to combine. Add vanilla extract and salt, and mix with a wooden spoon or spatula to combine.
While still hot, pour the frosting right over the cake. Move the bowl back and forth as you pour to ensure even distribution. Let the iced cake stand until the frosting is set, then slice and serve. Enjoy!