Made by toasting a rectangular slab of "mochi" paste in a Belgian waffle maker or a special moffle machine, the moffle is served as a dessert with ice-cream or chocolate sauce, or as a savory snack with cheese, ham or cod roe.
Bloggers are swapping tips on making "moffles" using ordinary waffle makers, cafes in Tokyo are offering daily moffle specials, and one company even launched a "moffle maker", Japanese media reported.
A spokesman for Sanyei Co, which produces the moffle maker, said demand took off in December and January, and there are now hardly any moffle makers left in stock, the Japan Times reported.
"It was something new, looked cute and was delicious," the newspaper quoted a moffle cafe owner as saying.
One blogger compared the taste of the crispy moffle crust to puffed rice encasing a chewy paste.
Mochi, mostly sold as soft, round little cakes, are among Japan's most popular sweets, although every year there are reports of elderly people choking on the chewy, sticky mass.