Preheat the oven to 350. Cream the butter and the sugar until
smooth. Add the 1/3 cup cocoa powder and mix until incorporated.
In a separate bowl, combine the flour, salt, baking soda, and baking
powder. Add to the butter mixture and mix until just combined.
Roll into small balls and make an indent with your thumb in the
center of the ball. Bake for 7-9 minutes or until dry looking and
lightly cracked on the surface but still very soft. I left mine a little
bit underdone so they were softer and fudgier, almost like a
When they come out of the oven, press the centers down again to
make a more defined well for the frosting. Allow to cool.
Whisk the cocoa powder, powdered sugar, hot water, and vanilla.
Spoon the frosting into the centers of the cookies and add
sprinkles. Allow frosting to set before storing in tins.