I have my own little confectionery business and this is the recipe I use when making marshmallow fondant. It taste fabulous! It does not taste like the yucky stuff that you buy at the store. It is easy to make but a mess too!
Place the whole bag of mini marshmallows in a glass bowl with 2 Tbsp of water. Also add the 2 tsp of flavoring. Melt the marshmallows in 30 second intervals, stirring between until melted.
Coat the counter top with a thin layer of shortening. Pour out half the bag of sugar on top of shortening on the counter top.
Coat your hands very well with shortening. (this is when it gets sticky!)
Pour the whole bowl of melted marshmallows on top of the sugar. start to knead the sugar and marshmallows. Add the remainder of sugar and knead till all is mixed together. If the fondant becomes too dry when needing then add 1/2 Tbsp of water to the dough till it is nice and elastic, like play dough.
Rub out side of the fondant with a very thin layer of shortening and wrap with plastic. Store in an air-tight container. You can leave it outside the fridge for up to 2 weeks. After that you will need to place it in your fridge.
TIP: If you have a sturdy stand mixer with a dough hook you can mix it in there. I always add about 1/2 cup shortening if I mix the melted marshmallows and sugar together with my stand mixer. You will still need to pour it out on the counter and knead it but it won't be quite as sticky. Just make sure when you first start mixing it with the stand mixer that you don't put the head of it all the way into the bowl till it is mixed a little bit. If you do the sugar with cover it.