chicken gizzards
The muscular stomach of the chicken, firm and slightly chewy, with a robust, meaty flavour.
Chicken gizzards are not stocked in every supermarket, but butchers, Turkish, Eastern European and Latin American grocers carry them, and Asian shops often have them frozen. They need long, gentle cooking to become tender; any tough yellowish inner lining and sinew should be trimmed off first if they are not sold cleaned.
Substitute:
Chicken hearts come closest in firm bite and robust flavour and cook somewhat faster; duck gizzards work just as well. Chicken thigh meat will do at a pinch, but it is softer and milder, and the dish loses its characteristic chew.