A German text contains the following sentence.
Und das Beste an den Alpen sind ihre Hütten.
Clearly das Beste must be a singular quantity given the article. So why is sind used and not ist?
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This is similar to expressions like "Das ist/sind (article when needed) (noun)" and "Es ist/sind (article when needed) (noun)" behave like "There is" and "There are" in English, so you take the numer of the noun (that is assigned to the pronoun) and not the pronoun, so you just look at the right side. Compare:
There are three apples. Das sind drei Äpfel.
So in your example, we just take the number of the tastable real things (huts) and use it when conjugating the verb. We could say that it is more important for us that the verb has the number of multiple objects, when those are "assigned" to another noun or pronoun, e.g. "das sind Äpfel" or "das Schlimmste daran sind die Krankheiten, die ..."
As a rule of thumb, when the subject and the subject complement disagree in number (das Beste and Hütten in your example), Plural is used. For more info on this and other difficult questions of Plural/singular usage in German: http://www.canoonet.eu/services/OnlineGrammar/Wort/Verb/Numerus-Person/ProblemNum.html
As pointed out by Dan, the answer is given in Canoonet: "If Subject and Gleichsetzungsnominativ in a sentence do not have the same number, the finite verb is usually plural." And a similar example is provided:
Mein größter Besitz sind meine Kinder.
Subjekt und Gleichsetzungsnominativ mit unterschiedlichem Numerus in http://www.canoonet.eu/services/OnlineGrammar/Wort/Verb/Numerus-Person/ProblemNum.html
Thank you, Dan.