There are things to be known about cocoa. It goes without saying that baking does not concern itself with the kind of chocolate / cocoa mixes used to make hot chocolate. Cocoa powder for cooking comes in two forms - natural, unsweetened cocoa and Dutch-processed. The photo here shows that the Dutch processed is darker and is often used in cases where the recipe is aiming for a deeper, richer colour and flavour.
David Lebovitz - that fabulous creator of food, who enviably lives in Paris, explains it all in detailed clarity. Worth reading, and a visit to his site might be a little "rabbit hole" adventure as you explore his blog entries and wonderful recipes. In brief:
remember there IS a difference, and use what the recipe calls for
some sources say if the recipe calls for Dutch-process you can substitute natural cocoa powder, BUT not vice versa (yet as I noted on the Chocolate Cheesecake Cupcake recipe, I have been doing that for years with no poor outcome...)
cocoa typically found on grocery store shelves is natural unsweetened
common brands of Dutch-processed are VanHouten, Droste
Though many ATK pages are accessible only to subscribers, their resource on cocoa is free for you to study.
Here's another informative update from Food Bloggers Canada's Kitchen Geekery. While I report above having a preference for Dutch-processed, but not noticing a difference, turns out that because of the alkalinity of the two cocoas - and the other ingredients in a cake recipe - the wrong combo can make a difference in the cake's rise. Foodbloggers of Canada explains why…