Melt the 12 tablespoons unsalted butter in a small saucepan over low heat. Remove from the heat and add the 1 cup fresh mint leaves. Allow the mint leaves to steep in the warm butter for 30 minutes.
Pour the melted butter and mint leaves into a blender and process until smooth. About 1 minute.
In a medium bowl whisk together the 2 ¼ cups bread flour, ½ teaspoon kosher salt, and 1 teaspoon baking soda.
Add the butter/mint mixture to the bowl of your stand mixer. Add the ¾ cup brown sugar and ¼ cup white granulated sugar and beat with the paddle attachment on medium speed until smooth. Lower the mixer speed to stir and add in the 1 egg , 1 egg yolk, and 2 teaspoon vanilla extract. Mix until thoroughly combined, about 30 seconds.
Stir the dry ingredients into the wet ingredients until just combined.
Fold in the ½ bag Andes mint chips.
Wrap the dough in wax paper and refrigerate for at least 2-3 hours.
Preheat the oven to 375°F (190°C).
Scoop 2 tablespoon-sized mounds of dough onto baking sheets about two inches apart.
Bake for 10 - 12 minutes or until the edges are lightly browned. Allow the cookies to cool for at least 5 minutes before transferring them to a wire rack to cool completely.