Melt butter and chocolate together over very low heat on stove/or double broiler. Stir constantly. Whisk brown and granulated sugar into chocolate mixture. Then, add eggs one at a time, stir after each. Stir in vanilla.
In a separate bowl mix the salt, baking soda, cocoa powder and flour together with a whisk. Add to wet ingredients and stir just until combined.
Refrigerate dough for at least 30 minutes and up to one hour so that cookies will maintain their shape while cooking. The dough should be quite firm.
Roll dough between your hands into walnut or full teaspoon sized balls. Bake at 350 for 8-9 minutes.
Cool cookies on pan for 5 minutes, then transfer to a wire rack. Allow to cool completely before filling.
Chop peanuts into small pieces.
Lie cookies out on their tops on parchment paper or a clean baking sheet.
Beat cream cheese and butter together until fluffy. Add peanut butter and powdered sugar, beat until well combined.
Spoon filling mixture into large freezer ziplock bag or piping bag. Pipe filling onto one cookie, place a second cookie on top of the filling to create a sandwich.
Roll edges where filling sticks out into salted peanuts. Repeat with remaining cookies.