Extremely hot (8)
'extremely hot' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for baking that I've seen before include "Cooking by dry heat" , "Making bread, cakes etc" , "Very hot (in the kitchen?)" , "theme in Hollywood TV shows" , "Making, eg, cakes" .)
(Another definition for sizzling that I've seen is " Noise of oil in a hot pan".)