Jack who stole those tarts? (5)
I believe the answer is:
knave
'jack' is the definition.
(knave can mean a jack playing card)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for knave that I've seen before include "Scoundrel - card" , "Rapscallion" , "Jack - scoundrel" , "Rascal; picture card" , "A swindler" .)