One showing Mary pastry case from trattoria (5)
I believe the answer is:
'one showing mary' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'pastry case from trattoria' is the wordplay.
'pastry' becomes 'pie' (pie is a kind of pastry).
'case from' suggests removing the centre (the case or outside of the word).
'trattoria' with its centre removed is 'ta'.
Can you help me to learn more?
(Other definitions for pieta that I've seen before include "Devotional painting" , "Status of Virgin with body of Christ" , "Religious figures" , "religious picture?" , "Sculpture of Mary with Christ's body" .)