Place the cream, marshmallows, icing sugar and salt in a large, deep saucepan.
Heat over medium-low heat, stirring often, until the marshmallows melt completely.
Remove from heat and stir in vanilla and food coloring (if desired).
Pour your icing into your mixing bowl and chill for a few hours to overnight. (Thoroughly chill).
Remove from the fridge and mix icing using an electric mixer or a stand mixer with a paddle attachment. (Icing will be stiff and difficult to stir by hand). Ensure all icing is mixed by scraping down the sides of the bowl at least once.
Beat for about a minute, until the icing becomes smooth and glossy. The icing will become quite thin - this is okay! Once it's smooth set the icing aside at room temperature for about an hour. It will thicken to a spreadable or consistency.
Spread or pipe the icing on top of cupcakes or other treats. Enjoy!