Is are dumplings/snails

[Rachel Adams]

I am confused by the combination of "food" and plural form of "smails" and "dumplings". Are both "is" and "are" correct?

1. "My favourite food is/are dumplings."

2. "The most unusual food I have ever eaten is/are snails."

"Many people think hamburgers are an American food." This sentence is from the book "Reading Challenge" by Casey Malarcher. So both constructions are correct, aren't they?

 

[5jj]

My favourite food is dumplings.
Dumplings are my favourite food.

The most unusual food I have ever eaten is snails.

Many people think hamburgers are an American food.

I have underlined the subject of the verb in each sentence.