Butter a 9 x 13-inch baking dish and set aside.
In a large saucepan, combine the sugar, evaporated milk, and butter.
Cook over medium heat, stirring frequently, until the mixture reaches 236°F on a candy thermometer.
Remove from the heat.
Add the marshmallow cream, chocolate chips, and vanilla.
Beat with a hand mixer until smooth and creamy.
Fold in the chopped pecans.
Pour the fudge into the prepared baking dish and spread evenly.
Refrigerate overnight until firm.
Cut into bite-sized squares.
Store in an airtight container or freeze for later.