Cream together the butter and sugar.
Add the egg and vanilla and mix together.
Mix together the flour, salt, baking powder, cinnamon, and cocoa powder. Sift together, into the wet mixture.
Mix together. I use a fork to stir and combine until it's crumbly, then use my hands to knead it into a dough ball.
Lightly flour a surface and, using a rolling pin, roll the dough flat. Aim for about ¼" thick.
Cut out your shapes. Roll the excess back into a ball, roll it flat again, and repeat, until all dough has been shaped as you like it.
(Optional) If you want to add sprinkles, lightly brush the cookies with a bit of water and add the sprinkles. This will make sure they adhere to the cookies.
Bake for about 9 minutes at 350° They won't look entirely done when you pull them out, but once you let them cool, they'll harden into a slightly crisp, soft cookie.