Toasts Ivy League university Head of Science (6)
I believe the answer is:
browns
'toasts' is the definition.
(brown can mean to toast or cook)
'ivy league university head of science' is the wordplay.
'ivy league university' becomes 'brown' (Brown University, part of US Ivy League).
'head of' indicates taking the first letters.
The first letter of 'science' is 's'.
'brown'+'s'='BROWNS'
(Other definitions for browns that I've seen before include "Beige and tan, e.g." , "Gently cooks" , "dark colours" .)