In a medium bowl, mix together the flour, cocoa, and salt.
In a separate bowl, mix together sugar, butter, vanilla, and egg with an electric mixer.
Slowly add the flour mixture to the bowl containing the sugar.
Add small amounts of peppermint extract until you like the flavor of the batter.
Take a spoonful of dough and flatten on cookie sheet about an inch apart.
Cook for 7-9 minutes at 350 degrees.
When they're done, remove them from the oven and immediately top with the crushed candy canes. The candy cane pieces may seem like they aren't sticking to the cookie, but they will after a few minutes of cooling. After 5 or so minutes on the cookie sheet, transfer to a wire cooling rack and enjoy!