Put the marshmallows, butter, dry food coloring and a couple of drops of lemon juice in a bowl. Set it over simmering water and cover, so the marshmallows swell from the steam. You can also melt them in the microwave.

Remove the bowl from the heat and gently stir with a spatula until you get an evenly colored marshmallow mass.

Gradually add the powdered sugar and knead the fondant by hand until smooth.

Use the fondant as needed. Happy decorating!