In a large bowl, whisk together the melted and cooled butter, granulated sugar, and brown sugar until the mixture has combined. Then whisking as hard as you can, whisk until the mixture starts looking light in color.

Add the egg, and whisk vigorously for 30 seconds. Then repeat with the egg yolk, whisk again.

Add the peppermint extract, vanilla extract, and milk. Whisk until smooth and slightly thickened. You should notice that the volume will increase the color will be lighter.

Add the flour, dark cocoa powder, salt, baking soda, baking powder, cornstarch, chopped chocolate bar pieces over the wet ingredients. Switch to a rubber spatula to gently fold the dry ingredients in until just combined and no streaks of flour remain. Making sure the chocolate pieces are evenly distributed throughout the dough.

Scoop the dough into large balls, like 4 tablespoons each, and place them on a parchment-lined baking sheet, leaving plenty of space between each one. I do 4 on a cookie sheeted. Place in the fridge for at least 30 minutes. Preheat the oven to 350F

Bake at 350°F for 10–12 minutes. When the centers look puffed and the edges are set, remove the cookie sheet from the oven and bang it on the counter three times. You don’t need to bang it too hard, but make sure it’s firm enough to create ripples in the cookies. You just want to remove the air. Return the cookies to the oven and bake for an additional 3 minutes, Take them out and bang them one more time. Place them back in the oven for 2 more minutes. Bake until the edges are golden brown and the centers are pale and slightly underbaked.

When done, let the cookies cool on the baking sheet. While the cookies are cooling, melt the white chocolate

In a microwave safe bowl, melt the white chocolate in 30 second increments, for 2 times, mixing between each increment, and then 10 seconds increments until the chocolate has fully melted.

Once fully cooled, dip each cookie halfway into the cooled melted white chocolate. Let excess drip off, then place cookies on parchment paper until the chocolate sets. Sprinkle crushed peppermint on top.

If you want a cleaner edge on the dip, you can spoon the white chocolate over the cookie rather than literally dipping it.

Let the cookies set completely before storing or stacking. You can speed this up by placing the tray in the fridge for 10 minutes.