Step 1

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.

Step 2

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.