Line a 9x13-inch pan with foil that hangs off the sides. Grease the pan and set aside.
Put the granulated sugar, evaporated milk, and butter in a large, heavy pot and bring it to a boil over medium heat stirring often. Boil for 5-6 minutes stirring often.
Remove from heat and add the semi-sweet chocolate chips, milk chocolate chips, marshmallow cream, and vanilla extract. Stir until smooth.
Spread the mixture in the prepared pan. Allow it to cool and become firm before cutting into squares.
Video
Notes
Store the fudge in an airtight container at room temperature for 1-2 weeks, in the refrigerator for 2-3 weeks, or in the freezer for 2-3 months.