Just a thought..
Instead of adjusting the single portion size of the recipe to fit into one birch-bark pot, would it be possible to make it the other way around? i.e. could the single portion size be split and cooked using two birch-bark pots (or however many needed to cook 1 portion), if I have 2 pots? Since crafting as many birch-bark pots as there are birch trees is way easier than buying even 1 iron pot.
Does that make sense?