In most sentences there is no personal pronoun as subject of the verb. The subject is just inferred. In this case "Lui" gets stressed very much. In combination with "come" the position of "lui" is either at the beginning, as given, or at the end. "Come descrive la ricetta lui?" If you put it behind "come" it will lose the stress and be dropped > "Come descrive la ricetta?"
It means how does he/she describe the recipe, just as it does when its "lui come descrive la riceta" the difference being in the latter is the emphasis on him/her answering it.
A situation like this would occur if you were to ask the question to someone, but someone else has answered on behalf, but yoj want to know how would THIS SPECIFIC PERSON answer the question.
I believe it is to emphasis it is He who describes the recipe. If you wanted to break it down, you could work from "Him/ how/ he describes/ the recipe". 'Come descrive la ricetta' does not specify a person, so it is ambiguous and could be he, she or it (a person or, perhaps, a book?) It probably also indicates that the person may have already been mentioned in the conversation.
Hopefully you know the answer after 3 years but for a newb I'll make it very simple. Think of verbs as containers, every verb contains either; I, you, (he, she, it), we, you all, they, them etc.. With that being said Come lui (descrive) = How does he (he,she, it describe). So to place proper emphasis "He" we begin with "Lui". "Does" of course is implied by the "?", so direct translation is somewhat confusing for traditional English speakers, He how (he, she, it) describe the recipe? Anyway, hopefully that wasn't confusing.
"descrive" is the 3rd person (he/she/it). "descrivi" is the 2nd person (you).
So, the literal translation is "He like/how describes the recipe", not "He like/how you describe the recipe".
I believe that, if you wanted to say "How does he describe the recipe", you could either say "Lui come descrive la ricetta" or "Come lui descrive la ricetta". If you wanted, in the latter version, you could drop the pronoun all-together and just write "Come descrive la ricetta". The difference between putting the pronoun (lui) before or after "Come" is for emphasis. If you put the pronoun before "Come", as was done in this exercise, it adds emphasis to the person describing the recipe. If you put the pronoun after "Come", there is not emphasis on the person who is describing the recipe.
Also, you don't always have to think of "come" as translating directly to "like". It can also translate to "how". Another way of thinking of "come" is to translate it, interchangeably, to "in the way that" or "in what way does". For example, I could say "lui mangia come io" and translate it to "he eats in the way that I (do)" rather than "he eats like I (do)". Or, I could say "come mangia?" or "come lui mangia?" and translate it to "In what way does he eat?" I could also say "lui come mangia?" to stress the pronoun which would translate to "in what way does HE eat?"
Describe the recipe: "It is a pan Asian fusion of vegetarian cooking" is a description. "It was vegetarian, very tasty and filling but it wasn't nicely presented" Those are both descriptions. though it would be more usual to ask "describe the dish/meal'. What is the recipe? Can you give me the recipe? Do you have the recipe? Yes 1 aubergine, 2 chillis; 1 onion; 100g of basmati rice etc. ..... (native speaker UK)