Insubstantial fare I prepare roughly about start of Christmas (4,5)
I believe the answer is:
rice paper
'insubstantial fare' is the definition.
(insubstantial food or fare)
'i prepare roughly about start of christmas' is the wordplay.
'roughly' indicates an anagram.
'about' indicates putting letters inside.
'start of' indicates taking the first letters.
The initial letter of 'christmas' is 'c'.
'i'+'prepare'='iprepare'
'iprepare' with letters rearranged gives 'riepaper'.
'riepaper' placed around 'c' is 'RICE-PAPER'.
(Other definitions for rice paper that I've seen before include "thin basis for dish" , "Thin edible base for baking" , "Cook it and eat it, don't write on it" , "baking aid" , "Thin edible sheet used in cooking" .)