• Line a 9×13 inch baking pan with parchment paper. Fold the parchment paper so that it fits snugly in the pan. I use two sheets – one folded to fit the length of the pan and another folded to fit across the pan. Allow the excess parchment paper to hang out over the side of the pan. Once the confection is firm, use the excess parchment to lift the whole block out of the pan to make it easy to cut into squares.
• Transfer the arrowroot cookies to a food processor and pulse until you are left with fine crumbs. Set aside.
• Place the butter, cocoa powder, and brown sugar into a large saucepan. Over medium-low heat, combine the two ingredients, stirring constantly, until the brown sugar has dissolved.
• Remove the butter mixture from the heat and stir in the peppermint extract and milk.
• Add the crushed arrowroot cookies to the saucepan and stir well to combine.
• Transfer the contents of the saucepan to the prepared baking pan and flatten to an even layer. Set aside.

For the Topping:

• Place the white chocolate chips, vegetable oil, and peppermint extract into a microwave-safe bowl. Microwave at half power in 30-second increments, stirring well between each increment until the mixture is melted and smooth.
• Pour the melted chocolate over the base layer and use an offset spatula to spread it out evenly.
• Sprinkle over the crushed candy canes and the M&Ms.
• Refrigerate for 4 hours before cutting into squares.
• Package in a food-safe container and keep refrigerated.