In large heavy pan heat sugar and evaporated milk until it boils stirring continuously with a wooden spoon. Set timer on stove and boil 7 minutes stirring continuously. You will see the color change to a darker cream color at the 7 minute mark. Place chocolate chips, butter and vanilla in a large bowl. Pour the milk mixture over the chips and stir gently just until mixed with the wooden spoon. Pour into buttered 9 x 13 pan and cover tightly with plastic wrap. Wait 24 hours. The fudge is ready to eat the next day.
Variations: Add nuts or dried fruit to the fudge.
This fudge is very creamy and can be kept in an airtight container for two weeks.