dododododododododododododdododododo you have many walnut trees in finland?
i've been reading an old cookbook that calls for walnut ketchup in many recipes, including one for an 18th c. rabbit curry, but i thought it was interesting how many ketchups people made in the past.
you need unripe and not ripe walnuts, but it looks quite easy to make and versatile in uses. according to other websites crushing the unripe nuts can stain your clothing, so be on guard!