Can you use either natural or dutch process cocoa? Any preferences?

As the recipe doesn't specify (in the version here or others on the web), use whatever you have on hand or prefer.

For the science and general recommendations, see this article from Serious Eats, which favors Dutch processed because only baking powder (not baking soda or both) is used here.

https://www.seriouseats.com/difference-dutch-process-natural-cocoa-powder-substitute#:~:text=If%20a%20cake%20or%20cookie,balance%20of%20acid%20and%20alkaline.