In a large heavy saucepan, heat the milk, brown sugar and salt until bubbles form around sides of pan. Whisk a small amount of hot mixture into the egg. Return all to the pan, whisking constantly., Cook and stir over low heat until mixture is thickened and coats the back of a spoon. Remove from the heat; whisk in peanut butter. Quickly transfer to a bowl; place in ice water and stir for 2 minutes. Stir in cream and vanilla. Press waxed paper onto surface of custard. Refrigerate for several hours or overnight., Fill cylinder of ice cream freezer two-thirds full; freeze according to the manufacturer’s directions. , When ice cream is frozen, spoon into a freezer container, layering with jelly; freeze for 2-4 hours before serving.