While the brownies cool, make the icing. In large bowl, beat butter, confectioners’ sugar, milk, vanilla and salt with an electric mixer until light and fluffy. Divide icing in half. Stir in half of the mini chocolate chips and chopped peanuts into half of the icing. Begin layering brownies with icing, spreading to edges and building up. Ice the top with plain icing and lightly crumb coat the sides. Drizzle caramel down the sides of the tower. Sprinkle the top with the remaining chocolate chips and peanuts.