Cookies

1. Preheat oven to 350°F. Line a baking sheet with parchment paper.
2. Place the chocolate chips in a microwave-safe bowl. Microwave for 20 seconds at a time, stirring after each interval. Continue microwaving until chocolate is melted and smooth.
3. Using a mixer, beat the butter and sugar until light and fluffy. Add the egg yolk and vanilla and continue beating until well blended.
4. Add in the flour, cocoa powder and salt and mix until combined.
5. Using a tablespoon, roll the dough into small balls. Roll each ball into sugar and place on the baking sheet. Indent each ball with your thumb or a 1/2 teaspoon measuring spoon. Note that the cookies will slightly crack around the edges.
6. Bake for 10-12 minutes or until firm. Cool cookies on the baking sheet for 5 minutes, then transfer to a cooling rack.

Filling

1. Add the white chocolate and heavy cream to a microwave-safe bowl. Heat for 20-30 seconds or until melted when stirred. One melted, stir in the peppermint extract and a few drops of green food coloring.
2. Fill the cookies with a spoonful of the mint filling. Place the cookies in the fridge for 30 minutes or until the filling has set. Top the cookies off with a drizzle of melted chocolate, if desired. 
3. Cookies will stay fresh for up to one week when stored in an airtight container in the fridge.