Melt the chocolate with margarine over a double boiler. Add the whipped topping (unwhipped) and nougat powder to the melted chocolate.
Add the ganache into a piping bag fitted with the decorative tip of your choice.
When the cream thickens, pipe onto your dessert. Decorate with a fresh leaf, attached with a dot of melted chocolate.
If the ganache is too loose, cool at room temperature (not in the refrigerator).