Preheat your oven to 350° F (180°C).
In the bowl of a stand mixer or with an electric hand mixer, cream together the butter, brown sugar and granulated sugar until well combined. Scrape the sides of the bowl.
Add in the egg and egg yolk, corn syrup and vanilla extract. Mix until well combined.
Add the all-purpose flour, cocoa powder, cornstarch, baking soda and salt. Mix until a soft dough forms.
Portion your dough into small 1 1/2 tbsp portions. Roll into a ball and then flatten slightly so it looks like a hockey puck.
Arrange on a parchment or silicone lined cookie sheet.
Bake at 350°F (180°C) for 8-10 minutes or until the cookies spread slightly and the edges start to crack. Pull the cookies out of the oven and let the cool on the pan.
While the cookies are cooling, make the toppings.
Start with the mint layer- in the microwave, heat 3 oz of heavy whipping cream (a scant 1/3 cup) until boiling (about 30 seconds).
Once heated, pour the white chocolate chips into the cream and allow them to sit for 5 minutes.
Stir until smooth, if the chocolate isn't completely melted, microwave the mixture for 15 seconds and then stir smooth.
Add the mint extract and one drop of green food coloring and stir to combine. Set aside and let the mixture cool until thick and spreadable.
Make the chocolate topping-in the microwave, heat 4 oz of heavy whipping cream (1/2 cup) until boiling (about 30 seconds).
Once heated, pour the semisweet chocolate chips into the cream and allow them to sit for 5 minutes.
Stir until smooth, if the chocolate isn't completely melted, microwave the mixture for 15 seconds and then stir smooth.
Set aside and allow the mixture to cool until thick and spreadable.
Once the cookies are cool and the toppings are thicker and spreadable, assemble the cookies by first spooning and spreading the green mint topping onto each cookie.
Allow the mint topping to sit on the cookie for about 5 minutes and then top with the chocolate topping, spreading to cover the top of the cookie.
Immediately sprinkle with chopped andes mint pieces.
Store in the refrigerator for up to 5 days or in the freezer for 3 months.