Measure and cook herb (6)
I believe the answer is:
dosage
'measure' is the definition.
(dosage is a kind of measure)
'cook herb' is the wordplay.
'cook' becomes 'do' (I've seen this in other clues).
'herb' becomes 'sage' (sage is a kind of herb**).
'do'+'sage'='DOSAGE'
'and' is the link.
(Other definitions for dosage that I've seen before include "Sea dog (anag)" , "quantity of drug" , "Measured portion of medicine" , "measure" , "The giving of medication in prescribed amount" .)