You can make the bars and topping ahead and store them separately for up to 2 days. Add the topping within a few hours of serving.   You can freeze the bars for 2-3 months. It’s best to freeze them without the topping and add it fresh before serving, but you can freeze them with the topping if needed. Freeze them unwrapped on a cookie sheet until solid, then wrap in plastic and foil or store in an air tight container.