Here's the deal. I'm a hobbyist and I love my dairy. I'm slightly obsessed with buttermilk. So I have never even attempted to make a dairy free cake. It just so happens that this coming weekend (July 2) my brother-in-law is marrying a wonderful girl who is highly allergic to anything milk based, chocolate, and tree nuts. She can have eggs, and said anything soy is fine, and they've asked me to make a cake for the rehearsal dinner. I tried to find a dairy free mix because I'm nervous about trying to change my recipes to dairy free, but had no luck. So does anyone have a tried and true dairy free recipe that's pretty sturdy? Flavor doesn't really matter, they just requested it be something that she can eat. Or can I just use one of my recipes and change from butter to soy margarine, and from milk to soy milk? I have a feeling it just won't be that simple because of the fats and what not, but honestly I don't know the science behind scratch as much as I want to, I just know my current recipes work.

I figured since ganache is out, I can just do an american buttercream (I loathe not being able to do SMBC), but I kind of detest all shortening, do you think the soy margarine would work here?

And I know to thoroughly wash all my pans and utensils beforehand.

I just want to do this where people can enjoy cake without having to have her bust out her epi pen!

Yes, you can change out the dairy products for soy products. My boss has two girls with severe peanut allergies, and one is also allergic to dairy. I use my regular poundcake recipe and swap out for the soy products. It doesn't change the flavor or even a noticeable change in the texture. They love it. I also use Sugarshack's buttercream recipe and use soy milk in that as well. Hope that helps.