Cake
Preheat oven to 350-degrees.
Grease and flour a 10" x 15" jelly roll pan.
Add the melted butter to a medium-sized bowl.
Next, add the sugar and mix well.
Now, add the eggs, one at a time, and mix well.
Add the cocoa and mix together.
Add the flour, salt, and vanilla and mix.
Finally, add the chopped pecans and fold into the mix. Pour the batter onto the jelly roll pan and bake for 15-20 minutes, or until cake tester comes out clean.
Once the cake cooks, add the marshmallows on top and place back in the oven for five minutes.
Remove from oven and set aside.
Frosting
Add the butter and milk to a saucepan on medium heat.
Once the butter melts, add the cocoa and vanilla. Mix together until all of the lumps are gone.
Pour over powdered sugar and mix together.
Finally, pour over the chocolate cake and marshmallows and let cool.
Serve!