The Expert Hostess 

Line a 13X9 inch pan with foil, letting the edges extend over the sides. Butter the foil and set aside.  Make the chocolate fudge:  In a medium heavy bottom saucepan over medium heat, melt the sugar, butter and milk, stirring constantly.  After the mixture begins to boil rapidly, until a candy thermometer reads 234°F.  I usually set a timer for 3 minutes once it starts boiling, and remove it from the heat when the timer goes off. Remove from heat and stir in chocolate, marshmallow fluff and vanilla, stirring until well combined.  Pour into prepared pan, spreading into an even layer. Immediately cover warm fudge with plastic wrap, placing the plastic wrap directly on the fudge. This will prevent it from developing a hard or crunchy top.

Make the peanut butter fudge:  In a medium heavy bottom saucepan over medium, melt the sugar, butter and milk, stirring constantly. After the mixture begins to boil rapidly, cook until a candy thermometer reaches 234°F.  Again, I set a timer for 3 minutes once it starts to boil. Remove from heat and stir in peanut butter, marshmallow fluff and vanilla, stir until well combined. Remove plastic wrap from chocolate fudge, and pour peanut butter mixture over chocolate layer, spreading into an even layer. Again, place plastic wrap directly on top of peanut butter fudge and set aside and allow to cool at room temperature. Cut into small squares and serve.