I found the Old Man's diary in the house near the cooking pot.
There's a recipe which will give you cold resistance. He says it uses raw meat, a spicy pepper and some other ingredient he can't remember.
What is the third ingredient?
OK, so I looked up the answer.
A Hyrule Bass caught in the lake West of the Temple of Time is what you need.
My question now is: How would I have known that on my own? I only found 3 peppers so I wouldn't have been able to experiment much with the ingredients I had. And it's unlikely I would've found that any time soon.
Is there any other hint that points you toward the third ingredient?