Preheat oven to 350°. Place cupcake liners in a muffin pan and lightly spray with cooking spray.
In a heavy-bottomed small saucepan, melt butter and chocolate over very low heat, stirring nonstop to prevent burning of the chocolate. Let cool slightly.
In a large bowl, combine sugar and eggs. Whisk together until smooth and light yellow, about 2 minutes.
In a medium bowl, whisk together flour, cocoa, and salt.
Slowly add chocolate mixture to egg mixture, stirring well. Mix in vanilla extract. Mix in flour mixture just until moistened.
Fill muffin cups about 3/4 full and bake for 20 to 25 minutes. Let cool.
To make Marshmallow Frosting, beat all ingredients using an electric mixer until smooth. Spread on cupcakes.
To make Mud Icing, combine butter and cocoa powder in a mixing bowl and using an electric mixer, beat until smooth.
Mix in milk and gradually beat in sugar and vanilla extract.
Top cupcakes with Mud Icing and pecans