A crust to eat — old woman digests it, on reflection (6)
I believe the answer is:
gratin
'a crust' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for gratin that I've seen before include "Au . . . . . . - cooked with a crust of melted cheese" , "'Au ..., with a cheesy topping (6)'" , "Cooked covered in grated cheese or breadcrumbs" , "Grated cheese or breadcrumbs on a dish" , "Au . . . . . ., cooked with a covering of cheese" .)