01 -
Preheat oven to 350°F (175°C) and line 2 baking sheets with parchment paper.
02 -
Using an electric mixer, cream together butter and granulated sugar until smooth, about 3-4 minutes. Add vanilla extract and egg, then beat until combined.
03 -
Add the all-purpose flour, cocoa powder, baking soda, and salt to the wet ingredients. Mix until a dough forms; it should hold together easily and be slightly tacky.
04 -
Roll the dough into 16 balls, approximately 1¾ inches in diameter. Place them on the prepared baking sheets and bake for 8-10 minutes, until the edges are set and the centers are slightly glossy. Let cool for 10 minutes before transferring to a wire rack to cool completely.
05 -
In a medium bowl, beat together powdered icing sugar, butter, milk, mint extract, and green food coloring (if using). Adjust consistency with additional powdered sugar or milk as needed. Spread evenly over the cooled cookies and freeze for at least 15 minutes.
06 -
In a medium bowl, combine semisweet chocolate and oil. Heat in the microwave in 30-40 second intervals, stirring between each, until melted and smooth.
07 -
Spoon the prepared ganache over the frozen cookies. Allow the cookies to thaw at room temperature before serving or store them as needed.