I am making All Occasion Downy Yellow Butter Cake, but since my daughter is allergic to milk, I need to substitute for the 1 C. milk.  My kids both passed allergy challenges so they can both have butter and eggs, but not milk. 
I had 2 ideas: substitute coconut milk for the dairy milk, but I am not sure about the taste.
or substitute 1 egg white plus enough water to make 1 cup liquid.  The theory behind idea 2 is replacing the protein lost in the milk with the egg. 
Any suggestions?

I have read in one of Rose’s books that goat milk can be substituted for milk.  But don’t rely on me, more informed people on this forum will be better sources of information. I hope it works out for you.

thanks for the tip.  The allergist said not to use any animal milk because the structure of the protein is smilar, so that will not work for us.  I’m just excited that my kids have outgrown enough allergies that I can bake with butter and eggs.

I understand the excitement! we too got a green light for baked egg just a few weeks ago. my son tolerated baked egg without incident in cakes and breads but our allergist took it off the table last year since he tested positive and he does react to straight up egg. fast forward year later with new allergist he says if it’s tolerated then we need to eat it.

i think coconut milk will be just fine. i’m not quite sure the exact science behind what the milk protein provides in terms of cake structure. i feel like milk may provide some tenderness to the crumb (BIG guess here). i know that from making wacky cake for my son all year the tenderness can be achieved w/out milk too. i once used coconut milk and a tablespoon of vinegar like the wacky cake and it worked very well.

if i were you i’d experiment a little if you can. cut a recipe in half so you don’t waste too much and try soy milk, coconut milk etc.

good luck!!

What about nuts- is almond milk a possibility?  Coconut milk sounds good, too.

rice milk ?

Well the Southern Coconut cake in RHC uses only coconut milk so Coconut milk should work fine (at least in cakes with egg whites).