The first flying saucer to serve up beancurd (4)
I believe the answer is:
tofu
'beancurd' is the definition.
(I know that beancurd can be written as tofu)
'the first flying saucer to serve up' is the wordplay.
'the first' becomes 't' (1st letter of 'the').
'flying saucer' becomes 'ufo' (synonyms).
'to serve up' is a reversal indicator.
'ufo' backwards is 'ofu'.
't'+'ofu'='TOFU'
(Other definitions for tofu that I've seen before include "Soya bean food" , "Curdled soybean dish" , "Cheese-like vegetarian food" , "Soy bean curd" , "Form of curd" .)