Pantomime dame's finale chasing the groom -- so funny! (6,5)
I believe the answer is:
mother goose
'pantomime' is the definition.
(I've seen this before)
'dame's finale chasing the groom so funny' is the wordplay.
'finale' suggests the final letters.
'chasing' means one lot of letters go next to another.
'funny' indicates an anagram.
The last letter of 'dame' is 'e'.
'the'+'groom'+'so'='thegroomso'
'thegroomso' anagrammed gives 'mothergoos'.
'e' after 'mothergoos' is 'MOTHER GOOSE'.
(Other definitions for mother goose that I've seen before include "[FAIRY STORY REF]" , "Imaginary author of a nursery rhyme collection" , "Pantomime" , "Panto" .)