He lost the knack of making pastry (4)
I believe the answer is:
tart
'making pastry' is the definition.
'tart' can be an answer for 'pastry' (type of pastry). I am not certain of the 'making' bit.
'he lost the knack' is the wordplay.
'lost' is a deletion indicator.
'knack' becomes 'art' (both can mean a skill or talent).
'the' with 'he' taken away is 't'.
't'+'art'='TART'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for tart that I've seen before include "The pastry sounds bitter" , "Acidic in taste" , "sour type of pie" , "Acidic - sweet pastry" , "Tom" .)