They soothe a temperature, tucking into round pastries (7)
I believe the answer is:
opiates
'they soothe' is the definition.
(opiate can mean anything which sooths or calms)
'a temperature tucking into round pastries' is the wordplay.
'temperature' becomes 't' (abbreviation).
'tucking into' is an insertion indicator.
'round' becomes 'o' (round can mean a round object).
'pastries' becomes 'pies' (pie is a kind of pastry).
'a'+'t'='at'
'o'+'pies'='opies'
'at' placed into 'opies' is 'OPIATES'.
(Other definitions for opiates that I've seen before include "Poppy-derived drugs" , "Is a poet (anag.)" , "Sedative drugs" , "Narcotic drugs" , "Drugs that dull the feelings, sedatives" .)