This is a pretty easy recipe to make and it tastes yummy too! The only thing I have to advise is that you WILL be a sticky mess. Another good tip: This recipe isn't so good for making decorations and letting dry out for a couple days to harden. I learned that the hard way. I use a totally different fondant recipe for making decorations. Also good to know, don't try to half this recipe. I learned that the hard way too! If you notice on Ethan's Birthday cake the black two is a little lumpy (yep that's the fondant I tried to make a half recipe of. Bad idea). I used it anyways because I didn't have time to go out and buy new stuff. I still think his cake was perfect though :)
Marshmallow fondant recipe (recipe from 
whatscookingamerica.net )
            MM       (Marshmallow) Fondant Icing Recipe  
            Ingredients:
                  16 ounces white mini-marshmallows(use a good quality brand)
      2 to 5 tablespoons water
      2 pounds icing sugar (please use C&H Cane Powdered Sugar for       the best results)
      1/2 cup Crisco shortening (you will be digging into it so       place in a very easily accessed bowl)
            
            Directions:
            NOTE:                     Please be careful, this first stage can get hot.
            Melt marshmallows and 2 tablespoons of water in a microwave       or double boiler. To microwave, place the bowl in the microwave for 30       seconds, open microwave and stir, back in microwave for 30       seconds more, open microwave and stir again, and continue       doing this until melted. It usually takes about 2 1/2 minutes       total. 
            Place 3/4 of the powdered sugar on the top of the       melted marshmallow mix.
        Now grease your hands GENEROUSLY (palms, backs, and in       between fingers), then heavily grease the counter you will       be using and dump the bowl of marshmallow/sugar mixture in       the middle. (By       the way, this recipe is also good for your hands. When I’m       done, they are baby soft.)
 
        Start kneading like you would bread dough. You will       immediately see why you have greased your hands. If you have       children in the room they will either laugh at you or look       at you with a questioning expression. You might even hear a       muttered, “What are you doing?”  
Keep kneading, this stuff is sticky at this stage! Add the       rest of the powdered sugar and knead some more. Re-grease       your hands and counter when the fondant starts sticking. If       the mix is tearing easily, it is to dry, so add water (about       1/2       tablespoon at a time and then knead it in). It usually takes me       about 8 minutes to get a firm smooth elastic ball so that it       will stretch without tearing when you apply it to the cake.
    It       is best if you can let it sit, double wrapped, overnight       (but you can use it right away if       there are no tiny bits of dry powdered sugar). If you do see       them, you will need to knead and maybe add a few more drops       of water.   
        Prepare the fondant icing for storing by coating it with a good       layer of Crisco shortening, wrap in a plastic-type wrap       product and then put it in a re-sealable or Ziploc       bag. Squeeze out as much air as possible.  
Here are a couple pics of Ethan's birthday cake and also his baptism cake to show you how lovely fondant can make a cake look:
                                        
Michelle