Marshmallow creme is a whipped, spreadable version of puffy marshmallows used in making fudge, frostings and other confections. Other interesting uses include smoothies, dessert sauces and a substitute for egg whites in a meringue pie topping.
This product is also sold under the names, marshmallow cream, and marshmallow fluff. It is usually found in the baking isle of most well-stocked grocery stores.
As a substitute for 1 cup marshmallow creme:
Solo Brand: Corn Syrup, Sugar, Water, Egg Whites, Artificial Flavor, Xanthan Gum, Lactic Acid, Salt. Contains Eggs.
Ingredients may vary per brand.
Makers of the old Marshmallow Fluff brand date their product back to 1917. The product was being made in the home of one Archibald Query and he was selling the product door to door. When WWI gets into full swing the eventual shortages made him close up shop. A few years later Alan Durkee and Fred Mower buy the formula for $500.00. The company went through some rough patches but eventually prospered and took off in the 1930's. You can read their complete marshmallow creme history here.
There are other brands of the product including Kraft (Jet-Puffed) and Solo.