Please see my answers in red.Which answer is better:
My favourite food is pizza.
Pizza is my favourite food.
Both are correct. Neither is better than the other.
Is it correct to list several things after "My favourite food is"?
My favourite food is pizza, spaghetti, fried chicken. No. You should amend it to read "my favourite foods are ....
What about countable nouns? Should I use the plural?
My favourite food is potatoes, carrots, tomatoes. Again, use the plural "..favourite foods..."
When I'm asked "What's your favourite book?" is it gramatically correct to say:
My favourite book is X, Y, Z and D. No.
or should I say:
My favourite books are X,Y,Z and D. Yes.
Interested in Language