There are several ways to make cocoa powder.  This article will reveal how to make cocoa powder from roasted cocoa beans.

I have written an article in which I explained  the process of making chocolate cream from cocoa. You can read the full article HERE

As you blend the roasted cocoa beans, it is going to be a dry blend at first. Further blending will make the blend pasty. So dont let the blend get pasty. The dry blend is the cocoa powder. To sweeten, you can add sugar, milk and other dry flavours and  blend.