Ate a cracking fish starter in restaurant, and to follow one beef dish (13)
I believe the answer is:
chateaubriand
'beef dish' is the definition.
(type of beef dish)
'ate a cracking fish starter in restaurant and to follow one' is the wordplay.
I cannot really see how this works, but
an anagram of 'ate' is 'tea' which is within the answer.
'a' could be 'an' and 'an' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for chateaubriand that I've seen before include "French writer" , "diplomat" , "Thick beef steak fillet" , "Fr. writer; fillet steak" , "French author" .)