Fact sheet
Rognons is the culinary term for an animal's kidneys, which belong to the "red" tripe group. Their quality stems in particular from the age of the animal and the way they are cooked. 

 

Taken from the animal's fifth quarter, they come in different shapes and sizes (lobed for beef and veal, similar to a large dried pulse for mutton) and were formerly considered a "commoner's" dish in Balzac's time.