Make a plain Bavarian; flavor with vanilla; divide it into three parts before the cream is added. Into one third stir one ounce of melted chocolate. Into another third mix two tablespoonfuls of pistachio nuts chopped fine, and color it green. Arrange the three parts in layers in a mold, beginning with the white, and stir into each one, after it has begun to set, and just before putting it into the mold, a third of the whipped cream. By keeping it in a warm place the Bavarian will not set before it is wanted, and it can then be made to set quickly by placing it on ice.