Line with parchment paper or apply the non-stick cooking spray in an 8×8-inch baking dish.
In a large mixing bowl, add in the chocolate chips, butter, and vanilla. Whisk until well mixed.
In a 6-quart saucepan, add in the milk, marshmallows, and sugar.
Place the saucepan on the stove and turn the heat to medium.
Allow the mixture to boil or until it reaches a temperature of 230 degrees F. Make sure to stir continuously for about 5 minutes.
Pour the mixture on top of the chocolate-butter.
Stir until well combined using a spatula.
Transfer the fudge into the prepared baking dish.
Let it sit for 1 hour until it becomes hard.
Remove the fudge from the baking pan and slice them into even pieces.
Serve and enjoy!
Note:
Place any leftovers in an airtight container, then place it inside the fridge.
