Step 1: Prepare the Dough

1. Preheat oven to 350°F (175°C). Grease or line a 9x13-inch baking dish with parchment paper.
2. In a mixing bowl, cream butter and sugar together until light and fluffy (2-3 minutes).
3. Add eggs, one at a time, mixing well after each. Stir in vanilla extract.
4. In a separate bowl, whisk together flour, baking soda, salt, and pistachio pudding mix.
5. Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Step 2: Bake the Bars

1. Spread the dough evenly into the prepared baking pan.
2. Bake for 20-25 minutes or until the edges turn golden brown.
3. Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Step 3: Make the Frosting

1. Beat butter until creamy.
2. Gradually mix in powdered sugar, heavy cream, and vanilla extract.
3. Spread the frosting evenly over the cooled cookie bars.
4. Garnish with chopped pistachios for extra crunch.

Step 4: Slice & Serve

1. Once frosting is set, cut into squares using a sharp knife.
2. Serve immediately or store for later (see storage instructions below).