To make the white chocolate coating, in the top of a double boiler or in a metal bowl set over barely simmering water, combine 6 ounces of the chocolate with the vegetable shortening. Melt over low heat, stirring, until it reaches 116 to 118 degrees F, or feels fairly warm but not hot to the touch. Remove from the heat and stir in the remaining 2 ounces of chocolate. Continue stirring until the chocolate reaches 80 degrees F or feels cool to the touch. Return to low heat and cook, stirring, until the temperature rises to 85 to 87 degrees F, or feels barely cool. Remove from the heat. This recipe calls for tempering the white chocolate. This step is not necessary unless you are going to store the turtles for longer than 1 week or if you desire a shiny, professional chocolate appearance. You may simply melt the white chocolate with the shortening in a double boiler over low heat and proceed as directed.