For the brownie layer:
10 tablespoons unsalted butter
1 cup granulated sugar
3/4 cup cocoa powder
1/2 teaspoon salt
2 teaspoons vanilla extract
2 large eggs at room temperature
1/2 cup all-purpose flour
1 package candy cane Joe Joes (or other chocolate-mint sandwich cookie)
For the cookie dough layer:
1/2 cup (8 tablespoons) unsalted butter, at room temperature
1/4 cup brown sugar
Scant 3/4 cup granulated sugar
1 egg, at room temperature
1 1/4 teaspoon vanilla extract
1 1/4 cup all purpose flour
1/2 teaspoon salt
1/2 teaspoon baking soda
1/2 teaspoon baking powder
1 cup of chopped peppermint cream candies (it is easier to cut them while they are cold)
To make the brownie layer:
Melt the butter in a medium-sized saucepan over medium heat. Turn off the heat. Whisk in the sugar and cocoa powder. Remove the pan from the burner and whisk in the eggs and vanilla until well-combined. Add the flour and whisk until it is fully incorporated. Set the brownie batter aside.
Preheat the oven to 350 degrees. Line a 9x9 pan with foil and leave an overhang so it is easy to lift the brownies out of the pan. Spray the foil with cooking spray.
To make the cookie layer:
In a mixer fitted with a paddle attachment, or with a hand mixer, cream the butter and both sugars until light and fluffy. With the mixer on low, add the egg and vanilla, making sure to scrape down the sides of the bowl. With the mixer on low speed, add the flour, salt, baking soda, and baking powder and mix until well combined. Fold in the mint creams.
Press the cookie mixture into the prepared pan into an even layer. Top the cookie dough with the candy cane Joe Joes in a single layer. Top the cookies with the brownie batter and use a spatula to spread the mixture evenly.
Bake for 30-35 minutes until a knife inserted in the center of the pan comes out clean. Let the cookies cool on a rack for 10 minutes before lifting out of the pan to cut and serve.