Makes one baking sheet of bark
1 pound white chocolate chips
1 pound dark chocolate chips or couverture disks
1 1/2 cups mini chocolate chip cookies
2/3 cup walnut pieces
1/3 cup mini chocolate chips
1 pound dark chocolate chips or couverture disks
1 1/2 cups mini chocolate chip cookies
2/3 cup walnut pieces
1/3 cup mini chocolate chips
Line a standard (18-x-13-inch) baking sheet with wax or parchment paper, and set it aside.
In a microwave-safe bowl, melt the white chocolate chips in 20-second bursts in the microwave, stirring after each heating. (Alternatively, melt in a double-boiler.) Drape a quart-sized plastic bag over a large cup or mug, then use a spatula to transfer the melted white chocolate chips into the bag.
In another microwave-safe bowl, melt the dark chocolate in 20-second bursts in the microwave (or over a double boiler), stirring after each heating, until just melted and liquidy. (See Recipe Notes for tempering instructions, if you'd like to do that!) Pour the dark chocolate onto the lined baking sheet, and using a spatula, spread it into an even layer about 1/4-inch thick.
Snip off a small corner of the bag with the melted white chocolate chips, then pipe it out onto the dark chocolate in 1/4-inch thick stripes, covering the surface of the chocolate. Drag a spatula through the stripes of white and dark chocolate, and then again going the opposite direction, creating a swirled pattern. Repeat down the length of the chocolate.
While the chocolate is still soft and liquidy, quickly press the mini chocolate chip cookies into the surface of the chocolate, spacing them about 1 inch apart. Sprinkle the walnut pieces and mini chocolate chips over top, and press the walnuts gently into the chocolate with the palm of your hand.
Place the sheet of bark in the fridge and allow it to set up for an hour, until completely solid. Cut or break it into large 2- to 3-inch pieces. Serve or store in an airtight container for up to 1 month.