Prepare the brownies as directed and allow to cool completely.
Spread the vanilla ice cream over the cooled brownies, then sprinkle the peanuts evenly over the ice cream. Place in the freezer until the ice cream is completely firm, at least 2 hours.
Meanwhile, make the topping. Combine the powdered sugar, evaporated milk, chocolate chips and butter in a medium saucepan over medium-high heat. Bring the mixture to a boil and cook for 8 minutes, stirring constantly. Remove from the heat and stir in the vanilla extract. Allow to cool for 30 minutes.
When ready, pour the chocolate topping evenly over the ice cream and peanuts. Return to the freezer for at least 2 hours, or until firm. Let sit at room temperature for 5 to 10 minutes before slicing and serving.