Line an 8-inch square baking pan with foil, extending it over the sides.
Use a double boiler to melt butter, stir in the sugar and cocoa. Whisk in the egg until the mixture is warm and the consistency of hot fudge, approximately 6 minutes. Remove from the heat.
Mix in the saltine crumbs and peanuts.
Press the crust into the pan. Set aside the saucepan of water to be used for the glaze.