Grease microwave proof bowl and spatula with vegetable shortening. Pour marshmallows and water into bowl then microwave on high for approximately one minute. Stir well for about one minute. Continue to microwave on high in 30 second intervals until all the marshmallows are melted.
Take out of microwave and add remaining ingredients except powdered sugar. At this point you can add any gel colors to your fondant in order to create uniform color, including white coloring to get a true white color.
Add half the bag of powdered sugar and mix until you can't mix anymore! Turn the mixture out onto the other half bag of powdered sugar you mounded on your counter.
Slowly knead the dough working from the outside in. Knead until you incorporate most all the powdered sugar.
Rub your hands with a generous amount of vegetable shortening and begin kneading the fondant until it's not coated in powdered sugar anymore and it becomes smooth. Continue to add a little vegetable shortening until it's pliable and smooth.
Coat again with vegetable shortening and wrap up in two layers of plastic wrap and then place in a zip lock bag overnight to rest.