In a mixer, cream together butter and sugar for approximately 2 minutes. Add cream cheese and vanilla and continue creaming for approximately 10 minutes. While creaming, set up a double boiler and slowly temper chocolate to melt. When completely melted, add into cream cheese mixture and mix until incorporated. Pour the mixture into the pie shell and smooth out top. Place in the refrigerator for at least 2 hours or until set. Cut into eighths and serve with your favorite fruit sauce. ~