Place bowl of marshmallows in microwave, and heat for 30 seconds.  Once done, stir and heat for an additional 30 seconds until marshmallows are melted.

Sift powdered sugar and spread about a cup on your counter to prevent fondant from sticking.

Pour half of your powered sugar on top of your bowl of melted marshmallows (leaving some powdered sugar remaining for the kneading process). 

Dump the bowl of melted marshmallows and sugar upside down on your counter.  This is messy, but that is normal!

WARNING:  THE MARSHMALLOW/POWDERED SUGAR MIXTURE IS VERY HOT AT THIS POINT.  BE CAREFUL AND DO NOT ALLOW CHILDREN TO KNEAD UNTIL COMPLETELY COOL.

Put a small amount of shortening on your hands and begin to knead the marshmallow/powdered sugar mixture on your counter.  You may think it will never come together, but it will!

Continue kneading. If the fondant is too soft, add powdered sugar and let cool in the fridge for 10 minutes.

Add food coloring at this stage. Twist and knead, until combined.

Knead until you have a smooth ball of fondant.  You will get a good arm work out!

With your surface still covered in powdered sugar, and your hands covered with a bit of shortening, roll ball of fondant out on the counter until you have a large flat circle of fondant about 1/4 of an inch thick.

Make sure your cake is covered in frosting (i.e. buttercream or cream cheese to keep the fondant secured to cake), and drape your rolled out fondant over your cake.

To get the sides of your cake nice and smooth, slowly push down on the fondant.  As you push your hands down, it will adhere to the sides of your cake all the way around.  Trim the excess on the bottom, and voila!