Cream butter, gradually add sugar, beating a medium speed of an electric mixer until well blended. Stir in chocolate and vanilla. Add 1 egg and beat 4 minutes, add remaining egg, and beat 5 minutes. Spoon mixture into graham cracker crust. Top with whipped cream. Chill 8 hours. (I prefer to freeze the pie because of the uncooked eggs. Defrost in refrigerator 1 hour before serving)
Graham Cracker Crust - Combine all ingredients, mixing well. Press into a 9" pie plate. Bake at 350 degrees for 8 minutes. Cool.