For the Cookies:

Preheat oven to 350

Mix butter with sugar until light and fluffy.  Add in the egg and vanilla.  Stir in the 2 oz of melted chocolate.  Add the flour, cocoa powder, baking powder, and salt.  This will form a stiff dough.  Divide the dough in two.  Place each dough ball between sheets of parchment and roll out to 1/8″ thickness.  Stack the rolled out dough and place in the refrigerator for one hour to chill.

Once chilled, use a 2″ round cookie cutter to cut dough and place round on a parchment lined cookie sheet to bake.  Bake for 7-8 minutes until set.  Allow cookies to cool on the baking sheet before moving them.

For the Filling:

Mix butter, powdered sugar, salt, and mint in the bowl of a stand mixer until very light and fluffy; 5-8 minutes by my watch.

For the Chocolate Topping:

Melt chocolate chips and oil until smooth using a double boiler or microwave.  I usually microwave for 30 seconds, stir, and microwave for 30 seconds more.

To Assemble:

Spread or pipe filling onto half of the cooled cookie rounds.  Top with the remaining rounds.  Dip each sandwich cookie into the melted chocolate covering one half of the cookie.  I like to leave half of the cookie uncovered so there is somewhere to hold on to the cookie without getting chocolate covered fingers!  Feel free to drizzle a decorative white chocolate on as well.