Combine sugar, milk and marshmallows in a pot on top of the stove. Bring to a boil and then turn to a low boil for 5 minutes or until mixture reaches the soft ball stage between 235-245 degrees fahrenheit on a candy thermometer. I just cook mine for 5 minutes stirring constantly to dissolve marshmallows.
While sugar mixture is cooking combine butter and chocolate chips in a microwave bowl and microwave on high for 1 minute until almost all melted. Remove and add vanilla extract and stir. Once sugar mixture is ready pour the two together and stir until smooth. Spray an 8 x 8 baking dish with cooking spray or line with foil and pour in fudge mixture. Refrigerate for at least one hour. Makes about 16 pieces depending on size you cut them.
Make this fudge peanut butter or butterscotch by just switching out the chips. This five minute fudge is so versatile and absolutely delicious.