If you can't access hyperlinked text, here's the URL of the article: https://www.realfastspanish.com/vocabulary/que-vs-cual
I'm grateful to DL for having us learn this phrase because it's different from English, as several people have pointed out. MichaelBell0's point about a prix fixe is probably most apropos for España or fancy restaurants. Some restaurants really do have different menus depending on the day, as is often the case when the menu depends on the fish caught that week or yesterday. So even in English in such situations we would say "What's the menu today?" although we often would say "What's on the menu?"
You can't really map qué and cuál to the English "what" and "which". They get used differently in different circumstances. Here you have a question of the form "¿Cuál es...?":
- ¿Qué es ...? - What is ...? (asks for a definition)
- ¿Cuál es ...? - What is ...? (asks for an answer); Which one is ...?
You can read on about the topic here.
The best explanation of the use of que vs. qual that I have seen is: Que es - asking what is the definition of Qual es - asking when there are multiple possible answers Qual de - asking which of these options is correct Que - required if immediately followed by a noun Que - if immediately followed by a conjugated verb and there is no clear choice Qual - if immediately followed by a conjugated verb and with a clear choice
Qué and cuál don't really correlate with "what" and "which" in English. When you have a "¿Cuál es ...?" sentence, you should choose the word that makes more sense.
- ¿Qué es esto? - What is this?
- ¿Cuál es esa montaña? - What is that mountain?
- ¿Cuál es tú bebida preferida? - What/which is you preferred drink?
- ¿Qué quieres comprar? - What do you want to buy?
- ¿Cuál quieres comprar? - Which one do you want to buy?
- ¿Qué animal eres tú? - Which animal are you?
- ¿Qué tan alto es? - How high is it?
You need to remember some rules, at least. There are two ways how you can think about it:
For one, you can think about what is being described. Ser (the verb that conjugates to es) is used to describe identities (what something is), characteristics (intrinsic properties), as well as the time and location of an event.
- Mi padre es médico. - My father is a doctor. (identity)
- El bosque es grande. - The forest is big. (characteristic)
- La reunión es el veinte. - The meeting is on the twentieth. (time of event)
Estar is used to talk about the state and condition of some object, as well as the location of some object.
- Mi padre está enfermo. - My father is sick. (state/condition)
- El bosque está cerca de la frontera. - The forest is close to the border. (location)
Or you could think about what kind of question is answered. This might work a bit worse, though. Ser answers the questions qué, cuál, and cuándo, so "what", "which", and "when". Estar takes care of cómo and dónde, "how" and "where". With very few exceptions.
Since the above sentence is talking about an identity (what = menu), and it asks the question cuál, the verb ser is used.here.
The way I remember it is that es is for things that are the characteristics of something, ie something that is inherent to the thing, ie the person is a doctor or the chair is green. Está is for the state of a thing, ie the lights are on, or the person is happy or at home.
Maybe this won't work for everyone, but it's a lot shorter and easier for me to remember than most of the explanations I've read.
In Spain the "menu del dia" is the daily special meal and typically includes a soup or salad, bread, a main course with a side dish, a dessert, and coffee. Wine or water is also included. Usually, you will have a couple of choices for the courses. Especially on the Camino del Santiago it is the cheapest way to have a good meal, and, at least for me, was always delicious. :-)