.Preheat oven to 350°F Line a 9×13-inch baking pan with aluminum foil, and grease lightly.
In a medium-large saucepan over low heat, melt together butter and chocolate, stirring occasionally. Whisk in sugar, salt and vanilla, then turn off heat. Whisk in eggs one at a time, waiting until each is fully incorporated before adding the next. Stir in flour and cocoa powder until mixture is uniform. Stir in peppermint oreo cookies and pour batter into prepared pan. Crush 3-4 additional cookies finely and sprinkle on top of batter, if desired.
Bake for about 35 minutes, until a toothpick inserted into the center comes out with moist crumbs, but not coated with batter.
Cool brownies in pan for about 20 minutes, then lift brownies in the foil out of the pan and place on a wire rack to cool completely before slicing.