Marshmallows are a sweet confection originating on Earth, consisting of sugar, syrup and water. They are normally white in color and cylindrical in shape. They are often used as a garnish for other desserts, or to complement hot, flavored beverages.
A popular way of preparing marshmallows is to lightly roast them over an open flame. Captain Spock supplied marshmallows (which he erroneously referred to as "marsh melons") for roasting during a visit to Yosemite National Park with Captain James T. Kirk and Dr. Leonard McCoy. (TOS movie: The Final Frontier) Members of the crew of the USS da Vinci also roasted marshmallows while camping on the planet Vemlar. (SCE eBook: The Art of the Deal)
Esperanza Piñiero claimed to have wanted to roast marshmallows over the flames of her Starfleet dress uniform, which she burned following her resignation. It was pointed out to her, though, that the burning uniform material would have given the marshmallows a bad taste. (ST novel: Articles of the Federation)
A popular dessert called "s'mores" is a sandwich of marshmallow and melted chocolate between Graham crackers. Marshmallow spread can also mixed with peanut butter to make "Fluffernutter". (ST reference: Star Trek Cookbook)