In a large bowl, mix together the butter and sugar until smooth and lightened in color. Add the eggs and vanilla and mix until just combined.
In a separate bowl, sift together all of the dry ingredients. Slowly add the dry ingredients to the wet ingredients and mix only until the ingredients are well incorporated. You don’t want to over mix this cookie. Add the mint chips and fold in to combine. Spoon onto a parchment lined baking sheet and bake for 8 minutes. Remove to a cooling rack.
For the frosting, place the white chocolate and heavy cream in a microwave safe bowl, and heat for 30 second intervals, stirring between each one until smooth and melted. Add the butter and powdered sugar to the chocolate and using a hand mixer, mix until smooth. Frost the underside of one cookie and then place another on top. Devour!