Preheat the oven to 350°F (175°C).

Line baking sheets with parchment paper or a nonstick baking mat.

In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.

Add the egg, egg yolk, and vanilla extract, and mix until well combined.

In a separate bowl, whisk together the flour, unsweetened cocoa powder, salt, baking soda, and baking powder.

Gradually add the dry ingredients to the wet mixture using a hand mixer or spatula. Mix until a thick dough forms.

Fold in the mint chips, chocolate chips, and chopped chocolate bar.

Scoop heaping tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.

Bake for 10–12 minutes, or until the edges are set and the centers look slightly underbaked (they’ll continue cooking as they cool).

Cool on the baking sheet for 5 minutes, then transfer to a wire rack.