Grease a 10x15 jelly roll pan.
Combine butter, sugar and evaporated milk into a dutch oven or other heavy duty (deep) pot.
Bring to a rolling boil and boil for 6 minutes.
Remove from heat and add marshmallow cream and chocolate chips.
Stir until it begins to thicken and then add the vanilla.
Stir until it no longer pours from the spoon and spead into greased pan.