Combine melted butter and cocoa powder. Stir until smooth.
Cream brown sugar and white sugar with the butter/cocoa mixture.
Add eggs and vanilla.
Stir in salt, baking soda, and flour.
Chill dough for 45 minutes. Preheat oven to 350 degrees.
Mix frosting ingredients and beat until smooth and creamy.
Scoop dough onto cookie sheets using a medium cookie scoop (2 Tbsp. size).
Bake cookies for 9 minutes.
As soon as cookies come out of the oven scoop 1 tablespoon of frosting onto each cookie. Allow cookies to sit 3 minutes to allow frosting to soften and begin to melt.
Spread frosting over cookies.
Sprinkle with chopped nuts, if desired.