• Line an 8x8 inch (20x20 cm) pan with parchment paper or aluminum foil, leaving an overhang around the sides.

Oreo Crust

• Crush the Oreo cookies (wafers and filling) in a food processor until they're fine crumbs. Alternatively, place in a freezer bag and crush with a rolling pin.
• Mix the crushed cookies with the melted butter.
• Press the mixture into the bottom of the prepared pan.

Peanut Butter Layer

• Beat together the softened butter and brown sugar until smooth.
• Beat in the peanut butter and salt until you do not see any lumps of butter.
• Mix in the powdered sugar about ½ cup at a time. It should be difficult to incorporate all of the powdered sugar and the mixture shouldn't stick to your fingers if you squeeze it.
• Spoon the peanut butter mixture over the Oreo crust and spread/press into an even layer. You can use a piece of wax paper to do this as well.

Chocolate Layer

• Chop the chocolate into very fine pieces and place in a heat proof bowl.
• Microwave on medium power (not high, which is often the default) for 45-seconds at a time, and stir between each interval until the chocolate is melted. Alternatively, melt in a double boiler over low heat. Stir in the shortening.
• Pour the warm chocolate over the peanut butter layer and smooth the top.
• Let the chocolate harden (either on the counter at room temperature or in the fridge). If placing in the fridge, not that the chocolate may discolor.

Slicing

• For easier slicing, when the chocolate looks about 90% hardened, score the top with a thin sharp knife where you plan to slice the bars.
• Once the chocolate has fully hardened, lift the bars out of the pan using the overhang of the parchment paper/foil and place on a cutting board.
• Slice the bars using a sharp, thin knife.