Which marshmallow-and-crisp-rice snack was invented by Kellogg employees in 1939?

The marshmallow-and-crisp-rice snack invented by Kellogg employees in 1939 was Rice Krispies Treats.

Kellogg employees Malitta Jensen and Mildred Day developed the recipe in the company’s kitchens in Battle Creek, Michigan. It combined Rice Krispies cereal with melted marshmallows and butter or margarine, creating a simple mixture that could be pressed into squares. The recipe was initially used as a promotional vehicle for the cereal and was publicized in advertisements by 1940.

Kellogg later used names such as “Rice Krispies Marshmallow Squares” and “Marshmallow Crispy Treats.” The packaged product was not commercially produced under the Rice Krispies Treats brand until 1995, even though home cooks had been making similar squares for decades. In Canada and the United Kingdom, the product is commonly called Rice Krispies Squares, while Australia and New Zealand use the name LCMs.