Preheat your oven to 350°F (175°C) and prepare a 9×13-inch baking pan by greasing it with butter or lining it with parchment paper.

In a large mixing bowl, cream together 1 cup of softened unsalted butter and 1 cup of granulated sugar using an electric mixer for 2-3 minutes until light and fluffy.

Add 2 large eggs one at a time and blend well, then stir in 1 teaspoon of vanilla extract until combined.

Add the entire box of 3.4 oz instant pistachio pudding mix and mix on low speed until fully incorporated.

In a separate bowl, whisk together 2 cups of all-purpose flour and 1 teaspoon of baking powder, then gradually add to the wet ingredients until a soft dough forms.

Spread the dough evenly in the prepared baking pan with a spatula and press gently.

Bake in the preheated oven for 22-26 minutes, checking for golden edges and a firm center.

Allow the bars to cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.

Prepare the glaze by whisking together 1.5 cups of powdered sugar and 2 tablespoons of milk until smooth.

Once cool, pour the glaze over the bars and spread evenly, then sprinkle ¼ cup of crushed pistachios on top.

For cleaner cuts, chill the bars in the refrigerator for 30 minutes, then slice into 24 squares.