Place vanilla, marshmallow cream and chocolate chips in a large mixing bowl and set aside.
Mix sugar, evaporated milk and 2T. butter in a 5 to 6 quart saucepan. Bring to full rolling boil over med. high heat, stirring constantly. Continue to stir and boil until reaches 233 degrees on candy thermometer. Approx. 8 minutes.
Add remaining butter to boiling mixture and heat until melted. Bring back to boil stirring constantly. Immediately pour hot mixture over ingredients in the mixing bowl. Stir until blended and all chips are melted.
Pour into a buttered 9 x 13 inch pan. Cool and cut into squares