1. Position a rack in the middle of the oven and preheat the oven to 350F. Have ready 2 unlined baking sheets.

2. In a medium bowl, combine the flour, baking soda and salt. Sift the cocoa powder into the flour mixture and set aside.

3. Using a stand mixer on low speed, mix the melted butter, sugars, water and vanilla extract until smooth, about 30 seconds, stopping the mixer to scrape the sides of the bowl as needed. Add the flour mixture, mixing just until the flour is incorporated, 25 to 30 seconds. Stir in 1 1/2 cups of the chocolate chips.

3. Leaving a 3-inch margin on all sides, use a thin spatula to spread half the dough on one baking sheet into a rectangle that measures about 11 x 8 inches and is about 1/4-inch thick. Use your palms to help pat it into an even layer. Repeat with the remaining cookie dough on the second baking sheet.

4. Bake one sheet at a time, about 14 minutes, or until the top looks dull, not shiny, and feels evenly firm at the edges and center. As soon as each baking sheet comes out of the oven, sprinkle half of the remaining chocolate chips over the cookie slab. Let the chocolate chips sit for 5 minutes to soften and melt, then use a small spatula to spread the melted chocolate over the cookie, covering most of the slab. While the chocolate is still warm, sprinkle half of the peppermint candy evenly over it.

5. Let the cookie bark cool on the baking sheets on a wire rack until the chocolate topping is firm, about 2 hours. Or, to speed the cooling, cool the cookies on the baking sheets for about 30 minutes, then refrigerate them, still on the baking sheets, just until the chocolate topping firms, then remove from the refrigerator. The cookie bark will become crisp as it cools.

6. Break each cookie slab into about 1 dozen 5- to 6-inch-long irregular pieces. Store cookies in a tightly covered container, layered between sheets of wax paper, at room temperature for up to 5 days.