1. Heat the oven to 350⁰F. Grease and flour a 13-by-9-inch pan.
2. In a medium saucepan, combine the butter and the cocoa and cook over medium heat, stirring now and then, until the butter is melted and the mixture is well blended, 3 to 4 minutes.
3. Stir in the beaten eggs, vanilla, sugar, flour, salt, and pecans, and beat with a wooden spoon or spatula or with a mixer at low speed until the batter is well combined and smooth, and the flour has disappeared.
4. Pour the batter into the prepared pan and bake at the 350⁰F for 20 to 25 minutes, until the cake springs back when touched gently in the center and is beginning to pull away from the sides of the pan.
5. Prepare the frosting while the cake bakes; so that you will be ready to poor it over the hot cake.
6. In a medium bowl, combine the confectioners` sugar and the cocoa, and stir to mix them well.
7. Add the melted butter, milk and vanilla, and use a large spoon or mixer at low speed to beat everything together well. Set aside until the cake is done.
8. Remove the cake from the oven, scatter the marshmallows over the top, and return the cake to the hot oven form about 3 minutes, to soften the marshmallows.
9. Place the cake, still in the pan, on a wire rack or a folded kitchen towel.
10. Pour the frosting all over the marshmallow-dotted cake, and cool to room temperature.
11. Cut into small squares and serve.

Recipe Courtesy of Mansi @ Fun and Food Blog