Line a 9x13-inch baking dish with foil and lightly grease it, or use non-stick foil for easier cleanup. Set aside.
In a large, heavy-bottomed saucepan, combine the sugar, butter, and evaporated milk. Stir constantly over medium heat until the mixture comes to a rolling boil.
Once boiling, continue stirring constantly and let it boil for exactly 9 minutes. This step is key to getting the perfect fudge consistency.
Remove the saucepan from heat. Immediately stir in the marshmallow cream and chocolate chips. Keep stirring until the mixture is smooth and fully melted.
Stir in the vanilla extract and mix until fully incorporated.
Quickly pour the fudge into your prepared pan and spread it evenly. Let it cool completely at room temperature until set, take several hours to set (about 4).
Once cooled and firm, cut into squares. Fudge can be stored in the refrigerator for up to 2 weeks or frozen for longer storage.