In a medium bowl, combine the flour, cocoa powder, salt, and baking power and set it aside.
In a small bowl, mix together the sugar and cinnamon. Set aside.
in a stand mixing bowl, cream together the butter and sugar with the paddle until well combined.
Add the eggs and mix with the whisk attachment on medium for 7-8 minutes or until pale and fluffy. Scrape down the bowl to make sure it is all incorporated before moving on.
Stream in the melted chocolate and vanilla and mix on low until combined.
Sift in the dry ingredients then fold them in gently with a rubber spatula until just combined.
Lightly brush a small amount of melted butter into each mold. This will keep them from sticking to the pan after baking.
Use a piping bag or a tablespoon to fill each mold ¾ full with the batter.
Bake at 350F/177C for 18-20 minutes or until you can touch the top and the cake springs back.
Let them cool for 5 minutes, then working one at a time, carefully remove each cookie and roll it in the cinnamon sugar. If you wait too long to roll them or let them cool too much, the sugar will not stick to the cake!
Drizzle with melted chocolate chips if desired.