Combine flour, cocoa, salt, and baking soda in a small bowl.
Cream together butter and sugar in a large bowl. Add eggs and vanilla one at a time and beat until incorporated.
Slowly beat in flower mixtureuntil dough is mixed and smooth.
Cover bowl and cool in fridge for 20 minutes.
While dough is cooling, preheat oven to 325ºF and prepare 3 or so baking sheets with foil.
Also, while dough is cooling, you can make the filling: beat powdered sugar, remaining butter, and vanilla and peppermint extract in a medium bowl until smooth and thick.
Remove dough from fridge, roll into balls a little smaller than a ping pong ball. Flatten on cookie sheets with your palm to about 1/2 cm thick. (Pretty thin.)
Bake 17 minutes.
Remove from oven and let cookies cool on a cooling rack for about 5 minutes. Then let them cool, flat, in the fridge for another 10-15 minutes. (This hardens them so that they don't break while you add the filling and glaze.)
You can make the glaze while they are cooling: melt chocolate chips in a double boiler until completely smooth. (That's it. Super easy!)
Spoon a dollop of melted chocolate on top of each cookie and sprinkle the crushed candy cane on top of each before the chocolate hardens.
Enjoy! Keep in the fridge so that they don't melt, I think they're better cold, just like Thin Mint Girl Scout Cookies ;)