Start by lining a 9x13-inch baking dish with parchment paper. This will help you lift the fudge out easily once it has set. Allow some overhang on the sides for easy removal.
In a medium saucepan, combine the butter, evaporated milk, and granulated sugar. Place the saucepan over medium heat, stirring frequently until the ingredients are melted and combined.
Once the mixture has combined, increase the heat and bring it to a gentle boil. Continue to stir constantly to prevent the mixture from scorching on the bottom. Allow it to boil for about 5 minutes, or until it reaches a temperature of 234°F (soft ball stage) if you're using a candy thermometer.
After boiling, remove the saucepan from heat. Stir in the chocolate chips, vanilla extract, and marshmallow cream. Stir vigorously until the chocolate chips melt and the mixture is smooth and glossy.
Carefully pour the fudge mixture into the prepared baking dish, smoothing the top with a spatula. Give it a gentle shake to level it out.
Allow the fudge to cool at room temperature for about 1 hour. Afterward, place it in the refrigerator for an additional 2 hours or until fully set.
Once the fudge is firm, use the parchment paper to lift it out of the baking dish. Cut the fudge into squares or rectangles, and enjoy! Store any leftovers in an airtight container at room temperature.