Comedian takes extremely large piece of cake (6)
I believe the answer is:
doddle
'piece of cake' is the definition.
(both can mean something very easy)
'comedian takes extremely large' is the wordplay.
'comedian' becomes 'Dodd' (Ken Dodd).
'takes' means one lot of letters go next to another.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'large' with its middle taken out is 'le'.
'dodd'+'le'='DODDLE'
(Other definitions for doddle that I've seen before include "Easy crossword?" , "Piece of cake" , "Something easily done" , "In slang, an easy task" , "Easy task (informal)" .)