In medium pan, combine marshmallow cream, sugar, milk, butter and salt. Bring to FULL BOIL, stirring constantly, over moderate heat. BOIL 5 MINUTES, over moderate heat, keep stirring. *(this is the hardest part of the recipe)
Remove from heat, quickly add chocolate chips; stir until chocolate is melted and mixture is smooth.
Stir in nuts and vanilla. Pour into greased 8" square pan, cool to room temp. Chill until firm and cut into squares.