• Line an 8×8-inch baking pan with parchment paper, leaving an overhang on two opposite sides for easy removal. Lightly spray the parchment with cooking spray.

Shortbread Crust

• Add the shortbread cookies to a food processor and pulse until fine crumbs form. Add the sugar and melted butter, then pulse until the mixture is evenly combined and resembles wet sand. (You can also crush the cookies in a zip-top bag with a rolling pin.)
• Press the crumb mixture firmly into the prepared pan using the bottom of a measuring cup or your hands to create an even layer. Freeze for 15 minutes.

Custard Layer

• In a large bowl, whisk together the vanilla instant pudding mix and cold heavy cream until smooth and thickened. Spread the custard evenly over the chilled crust.
• Refrigerate for at least 10 minutes while you prepare the ganache.

Chocolate Ganache

• Place the chocolate chips in a heatproof bowl. In a small saucepan, heat the heavy cream over medium heat until just simmering.
• Pour the hot cream over the chocolate and let it sit for 1 minute. Whisk until the chocolate is completely melted and the ganache is smooth and glossy.
• Let the ganache cool for 3 to 5 minutes. (Cool for closer to 3 minutes for a smoother top, or closer to 5 minutes if you want to create swoops.)

Assemble and Chill

• Pour the ganache over the custard layer and gently spread it into an even layer. If desired, use the back of a spoon to create a decorative swooped pattern.
• Refrigerate the bars for at least 2 hours, or until fully set. Use the parchment overhang to lift the bars from the pan and cut into squares. Wipe the knife clean between cuts for neat slices.