Step 1: Prepare the Sugar Cookie Base

1. Preheat oven to 350°F (175°C).
2. In a large mixing bowl, cream together butter and sugar until light and fluffy.
3. Add egg and vanilla extract; mix until well combined.
4. In a separate bowl, whisk together flour, baking powder, and salt.
5. Gradually add dry ingredients to wet ingredients, mixing until a dough forms.

Step 2: Bake the Cookie Layer

1. Line a 9×13-inch baking dish with parchment paper or grease it lightly.
2. Spread cookie dough evenly across the dish.
3. Bake for 18-20 minutes or until edges are golden brown.
4. Remove from oven and let cool completely.

Step 3: Make the Pistachio Pudding Layer

1. In a medium bowl, whisk together pistachio pudding mix and milk until thick.
2. Let the mixture sit for 5 minutes to set.
3. If desired, add powdered sugar for extra sweetness and mix again.

Step 4: Assemble the Bars

1. Once the cookie base is cool, spread pistachio pudding evenly over the top.
2. Sprinkle crushed pistachios on top for crunch.

Step 5: Chill & Serve

1. Refrigerate for at least 30 minutes to allow the pudding to set.
2. Drizzle melted white chocolate over the top before slicing (optional).
3. Cut into 12 bars and serve with whipped cream if desired.