In a large pot combine the butter, evaporated milk, and sugar.
Cook over high heat, stirring continuously until the mixture reaches 234 degrees (use a candy thermometer to keep track of the temperature).
Remove from heat.
Stir in chocolate chips until they are completely melted and completely mixed in.
Add vanilla; stir well.
Stir in marshmallow cream until it is completely mixed with the chocolate.
Pour fudge into a greased pan or serving dish.
Notes
I put it in the refrigerator to cool it quickly. It will take approximately 4 -5 hours to cool if you leave it at room temperature (which is way too long for my family to wait). Makes approximately 3 lbs.I like to buy Christmas tins at the post holiday sales when I can pick them up for a quarter. This recipe can be divided between 3 small tins and makes a delicious, inexpensive gift to share with the neighbors.