It's soft, that is, even when crusty (3)
I believe the answer is:
pie
'even when crusty' is the definition.
I can't tell whether this definition defines the answer.
'it's soft that is' is the wordplay.
'it's soft' becomes 'p' (musical abbreviation for 'piano').
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'p'+'ie'='PIE'
Can you help me to learn more?
(Other definitions for pie that I've seen before include "Pastry-topped dish" , "where blackbirds sang" , "Very easy answer as" , "Bird - dish - mixed type" , "Pastry crust with filling" .)