Electrical device cooked her toast (8)
I believe the answer is:
rheostat
'electrical device' is the definition.
(rheostat is a kind of electrical device)
'cooked her toast' is the wordplay.
'cooked' indicates an anagram.
'her'+'toast'='hertoast'
'hertoast' is an anagram of 'RHEOSTAT'.
(Other definitions for rheostat that I've seen before include "Resistor for regulating current" , "Sort heat with Instrument that controls the current in an electrical circuit" , "Current-changing device" , "Variable resistance" , "Variable resistor" .)