Combine the milk and gelatin in a double boiler and allow to set until firm.  Then simmer the water and cook gelatin until it is dissolved.
Add the corn syrup, butter, glycerin, vanilla, and salt and cook until the butter is almost completely melted, stirring frequently.  Set aside to cool.
Put TWO pounds of powdered sugar in large mixer bowl.  Strain the gelatin mixture into the powdered sugar.  Mix slowly with a batter blade until just combined.
Change to the dough hook attachment.  Slowly add 1-2 pounds powdered sugar.  The amount will depend on the humidity where you live.  I never get to 2 pounds.  You want the fondant to be firm and barely sticky.
Scrape fondant onto a heavily-powdered-sugared surface and knead it for a few minutes.
Take two pieces of plastic wrap, about 2 feet each, perpendicular to each other.  Spray lightly with nonstick spray.  Place fondant in center and fold wrap over fondant.  Store this in a large Ziploc bag or large airtight container.  Allow to set for 24 hours before using.