Q: This is how/what he likes his soup – hot and spicy wordreference.com:
(1a) This is how he likes his soup – hot and spicy.
It's said there (1a) is correct. But if I didn't know it, I would think it's incorrect, because when I met "how" it made me begin expecting that further in the sentence there would be some adverbial phrase which "how" is referring to, but then I suddenly saw the adjectives "hot and spicy" (instead of an adverbial phrase) and so was immediately very confused, because with adjectives I thought we must use "what" rather than "how".
To deal with it, I decided to compare "how" and "what" in this sentence. For this purpose, I made up several variants. Could you tell me please which of the next ones are correct and which are not and why?:
(1b) This is what he likes his soup – hot and spicy.
(2a) This is how he likes his soup – he locks himself in the kitchen and won't let anyone in until he's eaten it all.
(2b) This is what he likes his soup – he locks himself in the kitchen and won't let anyone in until he's eaten it all.
(3a) This is how he likes his soup – to salt a little and sprinkle with herbs.
(3b) This is what he likes his soup – to salt a little and sprinkle with herbs.
(4a) This is how he likes his soup – the way that no one else does.
(4b) This is what he likes his soup – the way that no one else does.
(5a) This is how he likes his soup – very-very much.
(5b) This is what he likes his soup – very-very much.

A: I can see your logic, but no, it's "how" every time.
The gap in your knowledge is that "how" does not only replace manner, but also quality.

— How was the trip you mentioned?
— It was amazing!

"What" replaces a noun phrase.

— What was the trip you mentioned?
— It was a school trip to Quebec!

It can also replace a verbal clause.

— What did you think of the trip?
— I thought it was exciting!

