Preheat and Prepare Pan: Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper or lightly grease it. This will help you remove the bars easily after baking.
Make the Cookie Dough: In a large bowl, cream together the softened butter and granulated sugar until light and fluffy. This should take about 2–3 minutes with an electric mixer on medium speed.
Beat in the eggs, vanilla extract, and pistachio pudding mix until smooth and fully combined. The pistachio pudding mix adds a delicious nutty flavor and helps keep the bars moist.
In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, mixing until just combined. Be careful not to overmix to maintain a tender, soft texture for the bars.
Bake the Cookie Bars: Spread the dough evenly into the prepared 9×13-inch baking pan. Use a spatula to smooth the surface. Bake for 20–25 minutes, or until the edges are lightly golden and a toothpick inserted into the center comes out clean. Let the bars cool completely before frosting.
Make the Frosting: In a medium bowl, beat the softened butter until creamy. Add the powdered sugar, pistachio pudding mix, and vanilla extract. Beat until smooth and fluffy.
Gradually add 2 tablespoons of milk and beat until well combined. If the frosting is too thick, add more milk, a tablespoon at a time, until you reach your desired consistency. If you’d like a brighter color, you can add a few drops of green food coloring and mix until evenly colored.
Frost and Garnish: Once the cookie bars are completely cooled, spread the pistachio frosting evenly over the top. You can use an offset spatula or a butter knife to smooth the frosting. Garnish with chopped pistachios or colorful sprinkles for a festive touch.
Slice and Serve: Cut the bars into squares or rectangles and serve. These bars are perfect for a sweet snack, dessert, or even a holiday treat!
