Line a 9-inch square baking pan with foil, allowing the foil to overhang the edges.
This will make it easier to lift the bars out later.
For the crust, in a medium saucepan, combine the egg, 1/2 cup of butter, unsweetened cocoa powder, granulated sugar, and vanilla extract.
Cook and stir over medium-low heat until the butter is melted, and the mixture just starts to bubble.
Remove from heat.
Stir in the crushed graham crackers and finely chopped pistachios.
Press this crumb mixture firmly into the prepared pan.
For the filling, in a medium bowl, beat the softened 1/4 cup of butter, pistachio instant pudding mix, and half-and-half with an electric mixer on medium speed until well combined.
Gradually add the powdered sugar, beating until the filling is smooth and creamy.
Spread this filling over the crust.
Cover and refrigerate for at least 1 hour, or until it's firm.
For the topping, in a small saucepan, melt the bittersweet chocolate and 1/4 cup of butter over low heat, stirring until smooth.
Spread this chocolate topping over the filling and sprinkle the coarsely chopped pistachios on top.
Cover and refrigerate for an additional 2 hours, or until everything is firm.
Using the foil overhang, lift the uncut bars out of the pan.
Cut into bars.
Notes / Tips / Wine Advice:
Storage:To store these delicious Pistachio Delight Bars, layer them between sheets of waxed paper in an airtight container and keep them in the refrigerator for up to 3 days. Enjoy!