Pistachio Pudding Sugar Cookie Bars

In a medium bowl, beat the softened butter until smooth and creamy, making sure there are no lumps. Add the powdered sugar, instant pistachio pudding mix, vanilla extract, and 2 tablespoons of milk. Beat until fully combined and smooth.Gradually add more milk, a small amount at a time, until the frosting reaches a spreadable, creamy consistency that holds its shape without being stiff. If desired, add a few drops of green food coloring and mix until the color is evenly distributed.
Frost and Garnish:
Once the cookie bars are completely cooled, spread the frosting evenly over the surface using an offset spatula or the back of a spoon. Work gently to create smooth, even coverage from edge to edge.Immediately sprinkle the chopped pistachios or festive sprinkles over the frosting while it is still soft so the topping adheres properly and adds texture and visual appeal.