Preheat the oven to 325º. Line a 9 x 13 inch baking pan with parchment paper and butter the paper.
In a microwave safe bowl add the butter and chocolate and cook on 50% power for about 2 minutes, stirring every 30 seconds until the chocolate has melted.
Whisk in the sugar, vanilla and salt. Add cold eggs, one at a time, whisking after each. Fold in the flour and mix, just until combined. Fold in the peanuts and pour into the prepared pan.
Bake for 25-30 minutes, until a toothpick comes out with just a few crumbs. Let it cool on a wire rack.
FROSTING: Once the brownies have cooled, add peanut butter and 6 tablespoons of softened butter to the bowl of an electric mixer, and beat until well blended. You can also use a hand mixer. Add powdered sugar, salt, and nutmeg and then add milk and vanilla. It should be thicker than frosting. Using an offset spatula or a knife, spread the frosting over cooled brownies.
GLAZE: Add 4 tablespoons butter and semisweet chocolate to a microwave safe bowl and cook at 50% power, stirring every 30 seconds until melted, smooth and shiny. Spoon it over the frosting and smooth with an offset spatula or knife. Refrigerate until the glaze has set, About an hour. If you wait too long and the glaze is hard, let it warm up until the glaze is pliable before cutting.