To assemble a double boiler, fill the bottom of a large pot with water and set another pot on top.
You can also use a heat-resistant bowl instead.
Make sure that the bottom of the upper pot or bowl is not touching the water.
Keep stirring the marsmallows till they are completely melted.
Add about half of the icing sugar and keep stirring till you get a thick and sticky mixture.
Make sure to wash your hands properly and spread some vegetable shortening on the working mat and on your hands so the mixture doesn’t stick.
Remove the sticky mixture from the bowl and place on the mat that has been well dusted with icing sugar.
Add the shortening and knead till it is smooth and no longer sticky to the touch. The fondant is ready to use.