Verbs that have stative meanings: mental state, emotional state, possession, sense perceptions and some other states. They are conditions or states and they do not progress. The food smells delicious. Smell is a natural thing we do not plan and it does not progress. Do a search for "stative verbs" and you will find interesting information.

Hi: "The food is smelling delicious" has a focus on an action that is taking place at the moment the words are spoken. The situation would be like this: Two people are sitting in the living room waiting for the dinner that Ann is cooking. One says to the other, "The food Ann is cooking is smelling delicious." "The food Ann is cooking smells delicious" could be used in the same situation. In this sentence there is no special focus on the time aspect (except that Ann "is cooking" the food right now). I would choose "smells delicious" as the most common way to express the idea; "is smelling delicious" is bound to the situation I described.

"Smells" is correct. In this case it is a STATIVE VERB (it describes a state of the food). There are well over 100 of these, but two categories of stative verbs are. 1) other senses: "looks" "sounds" "feels" "seems"; and 2) internal mental states: "believe" "know" "understand" "realize". So we usually say "She believes that I am honest" NOT "She is believing that I am honest".