Line an 8x8 baking pan with parchment paper. Use enough paper to leave a 1-inch overhang on each side. Alternatively, line a flat baking sheet with parchment paper.
Place the chocolate chips in a microwave-safe bowl. Microwave in 30-second intervals, mixing in between, until all the chocolate is fully melted and pourable. (Alternatively, use the double broiler method, see notes below).
Add the 15 chopped cookies to the chocolate and mix to combine. Pour the entire mixture into the 8x8 lined baking pan and spread evenly. Use a spatula to smooth out the top.
Sprinkle the additional finely chopped cookies on top. Let it sit for about 15 minutes, and then chill in the fridge for about 10 minutes or until the chocolate becomes solid (see notes below).
Lift the whole bark holding onto the paper overhang and cut into pieces with a knife! Store in an airtight container in the fridge until ready to serve.
The easiest way to melt chocolate is by using the microwave as instructed above, but be patient. If you over-heat or skip the mixing steps in between, the chocolate may overheat and clump.
If you want to use the double broiler method to melt the chocolate chips, see below on instructions for setup.
Allowing the Chocolate Bark to Settle - I'm pretty impatient when it comes to chocolate bark. So I end up leaving it out for 15 minutes and then placing it in the fridge so it settles quickly. But if you have the time, the ideal way to avoid imperfections in the chocolate is to let it cool at room temperature for a few hours.Storing - Although this Oreo Bark won't easily melt at room temperature, the only way to guarantee this is to temper the chocolate. Therefore, I'd recommend storing it in the fridge until ready to serve if possible.To Setup A Double Broiler:
Find one medium size pot and a metal bowl. The size of these two items should be such that when the metal bowl is placed on top of the pot, the two are nested together.
Add about 2 inches of water to a saucepan and simmer on low-medium heat.
Add the chocolate chips to another metal bowl.
Set the bowl on top of the pot with the simmering water so that the two pieces nest together. Note that the bottom of the metal bowl should not be touching the simmering water when nested together. If this happens, remove some of the water. The steam from the simmering water is being used to heat up the chocolate chips
Stir frequently until the chocolate chips are completely melted.