Spaghetti, perhaps - mostly cooked al dente - followed by a custard tart (6,2,4)

'custard tart' is the definition.
(type of Portuguese custard tart)

'spaghetti perhaps mostly cooked al dente followed by a' is the wordplay.
'spaghetti perhaps' becomes 'paste' (spaghetti is a kind of paste).
'mostly' means to remove the last letter.
'cooked' indicates an anagram (letters cooked into a new form).
'followed by' is a charade indicator (letters next to each other).
'paste' with its last letter taken off is 'past'.
'al'+'dente'='aldente'
'aldente' with letters rearranged gives 'eldenat'.
'past'+'eldenat'+'a'='PASTEL DE NATA'