How to say this in Japanese?

Hello!

Well, my mother tongue is not English, but I'll try to explain my doubt.

My friend's favorite icecream flavour is "butterfat" icecream. I don't know if the name in English is "butterfat" or just "cream". Anyway, how to say this icecream flavour in Japanese?

Thank you for your attention.

The word "butterfat" in Japanese is "nyuu-shibou", but I've never heard of butterfat-flavored ice-cream in any country. My understanding is that butterfat is almost always contained in ice-cream, but I've never seen it as a name of a flavor.

What is the flavor like? Are you sure it's buttermilk? Maybe you're talking about "condensed milk" which is sort of like thick sweetened milk. If so, in Japanese it is called "ren-nyuu".

Thank you for your big help!

That word in my mother tongue is "nata", it's in Portuguese.
I don't know if there is a translation to this in English.

Hmm, maybe you're talking about Pastel de Nata, which is a Portuguese specialty. I understand that you call them just "nata" in Portugal. Pastel de Nata is called Egg Tart in Japan, and pronounced like "eggu taruto".

I found a Japanese-language blog talking about an "ice-cream version of Pastel de Nata".
http://necopol.blog.so-net.ne.jp/2012-07-20

If this is what you're talking about, I don't think we have them in Japan, at least not commonly. But when explaining to others, I suppose you can say that you have "Egg Tart ice-cream" in Portugal.

I assume that the word "nata" itself just means "cream", so that doesn't really make sense either.

"Nata" by itself I think would be "cream" in English and 生クリーム (nama-kuriimu) in Japanese.
At least that's what we understand by "nata" in Spanish.
Cream flavored ice-cream is not that common, maybe the closest you will find is milk-flavored. Which would be ミルク (miruku) in Japanese.
If your friend comes to Japan, have him try the Cremia soft-serve ice-cream they have at some stores, it's more expensive than regular soft-serve but it does taste a lot like cream, I really like it! (I swear my reply is not sponsored in any way by them, lol)
https://www.nissei-com.co.jp/sweden/image/cremia.jpg

Uco and Ruby, thank you so much for your replies.