In a microwave-safe bowl, combine the dark chocolate, peanut butter, and butter. Melt in 20-second increments until melted.
Stir in the rolled oats, chocolate cookies, and confectioners sugar.
Transfer the mixture into a lined 8 x 8-inch pan. Let the bar base set until firm.
In a microwave-safe bowl, combine the chocolate and peanut butter until smooth and glossy. Pour over the top of the chocolate slice and refrigerate until firm.
Once firm, let it sit at room temperature before slicing and serving.
Notes
TO STORE: As this is a no bake dessert, the bars can be stored at room temperature in an airtight container. They will keep well for at least a week. If you'd like them to keep longer, store them in the refrigerator and they will keep well for at least four weeks. TO FREEZE: Place the slice in a ziplock bag and store them in the freezer for up to 6 months.