One leaving whole sheep's heart in dish (6)
I believe the answer is:
entree
'one leaving whole' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'sheep's heart in dish' is the wordplay.
'sheep's' becomes 'ewes's' (a ewe is a female sheep).
'heart' indicates the central letters.
'in' indicates putting letters inside.
'dish' becomes 'entre'.
The centre of 'ewess' is 'e'.
'e' put into 'entre' is 'ENTREE'.
(Other definitions for entree that I've seen before include "formal entrance" , "Introduction" , "Dish allowing one to go in?" , "Main course dish" , "Something that provides access" .)