Ok. I purposly do not own a microwave. Can mm fondant be done on a double boiler?
Don't see why not. It'll just take a little longer to melt them to the needed consistency before mixing w/ other ingredients.
Most definitely, like the pp said it does take longer and you have to be really careful not to burn the marshmallows, I overheated it a few times and it makes the final product really hard and hard to work with. When I add shortening rather than water to the marshmallows, it's easier all around.
Today was actually the first time I used the microwave previously I just used a pot not even my double-boiler! I just kept the heat on med. and stirred well with a silicone spatula. I then would take the pot off the heat and mix the icing sugar right in to the pot.