Preheat your oven to 350°F (175°C). Grease and flour the baking pan or line it with parchment paper for easy removal of the bars.
In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the egg and vanilla extract to the creamed mixture, beating well to combine.
In another bowl, whisk together the flour, baking powder, salt, and pistachio pudding mix until evenly blended.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined and a dough forms.
Spread the dough evenly into the prepared baking pan. If desired, sprinkle chopped pistachios on top for added texture and flavor.
Bake in the preheated oven for 25-30 minutes, or until the edges are lightly golden and a toothpick inserted in the center comes out clean.
Allow the bars to cool in the pan before cutting into squares. For an extra touch, dust with powdered sugar before serving.
Store leftovers in an airtight container at room temperature for up to 3 days.