Der Nutella-Brotaufstrich.

Two can play this game. There is no sane answer.

Except for rules of thumbs like "Romance-sounding word ending in -a is probably female".

My point is that, whenever you want to use a brand name like "Nutella" in a specific context and you're unsure about the gender, you can just use a compound word with a clearly defined gender instead.

Touché.

On a semi-related note: in the Rhineland gendered articles are also used colloquially when talking about people: "Der Mark", "Die Steffi" and so on. I was born into this but I'm unsure how I feel about it after finding out it's actually non-standard in the rest of Germany.