Like mad, tucked into favourite kind of teacake (7)
I believe the answer is:
pikelet
'kind of teacake' is the definition.
(type of crumpet)
'like mad tucked into favourite' is the wordplay.
'mad' indicates anagramming the letters.
'tucked into' is an insertion indicator.
'favourite' becomes 'pet' (synonyms).
'like' is an anagram of 'ikel'.
'ikel' placed into 'pet' is 'PIKELET'.
(Other definitions for pikelet that I've seen before include "15 [TEACAKE]" , "afternoon treat, perhaps" , "local crumpet" , "Type of crumpet" , "Thin kind of crumpet" .)