Place the marshmallows, jello and water into a glass bowl. Microwave for 30 seconds at 50% power and stir. Microwave again and stir completely.

Gradually add in ¼ of the powdered sugar and give it a good stir. It will be thick and sticky, but keep stirring. Add in a bit more sugar and when it gets too thick to stir, then transfer it to a silicon mat that's coated in shortening.

Knead more sugar in until it no longer sticks to your hands. You may not use all of the sugar or you may need to add a bit more sugar, it all depends on how thick you want your fondant.

Once it's at a thickness and consistency of play-doh, it's done.

To store your fondant, add some shortening to your hands and rub it over the fondant, wrap it with plastic wrap and then place it into a sealed bag, preferably one with a vacuum seal. Let your fondant sit overnight.