Wrap the bottom of a 10-inch tart pan in plastic wrap to prevent chocolate from leaking out. Pour about 3 cups of melted chocolate into the pan, spreading it to coat the bottom and the sides of the pan. Be careful not to leave any thin spots in this chocolate shell layer. Place the pan in the freezer for a few minutes to harden.
In a large bowl, combine the peanut butter and powdered sugar and fold in the mini cookie sandwiches.
Scoop the peanut butter mix into the tart pan, spreading it to the sides and smoothing out the top. Pour the rest of melted chocolate on top, smoothing it out and spreading it to the sides. Freeze again until the chocolate layer has hardened.