Ingredients

• Crust:
• 1 (9-ounce) package dark chocolate wafer cookies, finely crushed (about 2 1/3 cups crumbs)
• 1/2 cup melted unsalted butter
• 1 egg yolk
• Filling:
• 1/2 cup unsalted butter, melted
• 2 1/2 cups confectioners' sugar
• 1 1/2 teaspoons peppermint extract
• 1 1/4 teaspoons vanilla extract
• 1 to 2 tablespoons cream or milk, as needed
• 2 or 3 drops of green food coloring (optional)
• Topping:
• 9 ounces bittersweet chocolate, broken into bits, or 1 1/2 cups semisweet chocolate chips
• 1/4 cup unsalted butter, cut into bits
• Milk as needed
• Coarsely crushed red or green striped mint candy (optional)

Instructions

1. Make the crust: Preheat oven to 350 degrees F. In a medium bowl, combine crumbs with butter and egg yolk, stirring and tossing with a fork until ingredients are thoroughly mixed. Pat evenly over the bottom of an ungreased 13-by-9-inch baking pan. Bake for 8 minutes, or until crumb mixture is firm. Let cool completely.
2. Make the filling: Beat all ingredients together to make a smooth, easily spreadable buttercream. Spread evenly over cooled crust. Refrigerate for 20 to 30 minutes until buttercream is firm.
3. Make the topping: Place chocolate and butter in a microwave-proof bowl or in the top of a double boiler. Microwave on medium-high (80 percent) or heat over hot water, stirring occasionally, until melted and smooth. Chocolate should pour easily from a spoon; if necessary, thin with additional butter or a tablespoon or so of milk. Spread chocolate evenly over chilled buttercream. If desired, sprinkle crushed mint candy over the top.
4. Return cookies to refrigerator for at least 2 hours, until firm. Cut into bars; cutting is easier if you clean off the knife between cuts.