am making https://food52.com/blog/10307-flourless-chocolate-cake on the urgent fly. Not much of a baker, so don't know what I can substitute for Dutch

If you only have "natural," which is to say, "un-Dutched" cocoa powder, go ahead and use it. Flourless chocolate cakes contain no leavening, such as baking soda, which is the issue with Dutched vs. natural cocoa powders.

I think you mean Dutch processed cocoa powder -- do you have any cocoa powder? If not, I think it's worth a trip to the store to get cocoa powder (and no problem if it's not Dutch process).