Preheat oven to 350 degrees F and grease an 8x8 inch pan or line with parchment paper, leaving some overhang on the sides for easy removal.
Melt the butter, peppermint extract, and 2-oz (half a bar) of the white chocolate chunks in a double boiler, or gradually in the microwave for 30 second increments.
While chocolate and butter are melting, add cocoa powder, flour, and salt to a mixing bowl and whisk to combine. Set aside. Crush candies in a ziplock bag with a rolling pin or meat mallet.
When the butter is melted, whisk in the sugar until it's completely combined. Add eggs and vanilla and whisk to combine. Add in flour mixture and fold with a spatula. Finally, add most of the crushed peppermint candy and remainder of white chocolate chunks (reserve some crushed mints and chocolate for the top) and fold. Transfer batter to prepared pan and spread evenly. Batter will be thick. Sprinkle the remaining chocolate and candy on top.
Bake for approximately 35 minutes or until a toothpick inserted into the center comes out almost clean. You want there to be a few moist crumbs left on the toothpick. If toothpick comes out with wet batter, put back in the oven and test every couple minutes until done.
Transfer pan to a wire cooling rack to cool completely before adding the drizzle. When ready, melt chocolate chips in a double boiler and transfer to a squeeze bottle or ziplock bag with the tip cut off and drizzle it on the brownies.
I recommend cutting into 1-2 inch squares or bite-size pieces because these babies are rich! Cover and store at room temp for up to a week.