I started by crushing the peppermint. In order to do this, I simply put about 10-15 peppermint candies in the food processor and ground them into a nice peppermint dust.
Begin by combining the sugar, milk, butter, and cocoa in a medium saucepan and bring to a boil. Let this boil at least 1 1/2-2 minutes, I typically go with 1 1/2 minutes. Be sure not to let it boil over 2 minutes or they will not set correctly.
Remove from heat and stir in the peppermint, oats, and vanilla. Drop the cookies in tablespoon fulls on wax or parchment paper then let them cool until hardened. At this point, I almost always put mine in the fridge to harden.