My marshmellow fondant recipe is 16 oz. mini marshmellows, 1 Tbsp water, 3/4 bag of 2 lbs. confectioner sugar, 1 tsp. light corn syrup and 1 tsp clear flavor (I use vanilla)
Put mm in microwave safe bowl, pour water over and heat until melted.(Grease wooden spoon with shortening to stir mm) Stir in corn syrup and flavor (you can also put in coloring at this point if you need the whole thing one color - I normally color just the amount I need after its all mixed). Pour all this into bowl with confectioner sugar and mix with wooden spoon and then with your hands until no longer sticky and its a great big ball. (You can add confectioner sugar if needed)
I grease my table and hands as needed and knead to get it to the consistency (pliability) I want. The original recipe calls for it to be covered in a light coating of shortening overnight in a sealed container, but I used it Saturday after just making it and it worked wonderful.