Light, milk-based food with no topping (4)
I believe the answer is:
airy
'topping' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for airy that I've seen before include "Well ventilated; insubstantial" , "Spacious; delicate" , "Old astronomer" , "Spacious - aerial" , "Fanciful" .)