The last time I made marshmallow fondant, I used my Kitchen Aid mixer for mixing most of the sugar in, since I wanted to save time, and then just added a bit more sugar while kneading it on my silicone mat. It worked well, except the one thing you have to make sure of is that you add enough sugar and knead it long enough, or you will have air bubbles in your fondant when you roll it out. I have found out, that you can add more sifted sugar and knead it longer after you have let it set overnight. This way, you will have a nicer finish to your fondant. Click on this link for the complete fondant recipe:
Making marshmallow fondant
Melt mini marshmallows with water in microwave at 40 second increments, stirring after each.
When marshmallows are completely melted, add the corn syrup and flavoring. The mixture will look very soupy at this stage.
Sift powdered sugar into Kitchen Aid bowl. I use a simple metal strainer...works better than a sifter.
Pour melted marshmallow mixture into Kitchen Aid bowl with sugar.
Use dough hook on low speed to mix fondant mixture.
This is the consistency it should be when you are done mixing.
Scrape the fondant mixture out of the bowl with a plastic scraper onto a greased silicone mat.
Dust with sifted powdered sugar and begin kneading.
Knead until you have a smooth and elastic ball and the fondant no longer spreads as it sets.
Cover with Crisco and store in ziploc bag to rest overnight.
This is some black fondant made with Hershey's Special Dark cocoa.