Pre-heat oven to 350°
Using an electric mixer cream the butter and sugar until blended well
Add the vanilla extract and egg yolk, keep egg white in a bowl and set aside
Add the flour gradually and mix until combined
Add crushed peppermint (I use a food processor or coffee grinder to crush peppermint) Put extra sugar in a bowl and set next to bowl of egg whites
Whisk egg whites slightly; just so they are no longer liquid but not too frothy
Roll dough into 1 inch balls and dip into slightly beaten egg whites; then roll in the sugar
Top each cookie with a chocolate chip
Place on a baking sheet covered in parchment paper Bake for 12-15 minutes, until the bottom is brown and the edges are slightly