Cook lining up initially one type of pasta (8)
I believe the answer is:
linguini
'type of pasta' is the definition.
'cook lining up initially one' is the wordplay.
'cook' indicates anagramming the letters.
'initially' suggests taking the first letters.
'one' becomes 'i' (Roman numeral).
The initial letter of 'up' is 'u'.
'lining'+'u'='liningu'
'liningu' is an anagram of 'linguin'.
'linguin'+'i'='LINGUINI'
(Other definitions for linguini that I've seen before include "Italian course" , "dish in Milan?" , "Flat, thin pasta" , "food" , "Long thin pasta" .)