These crunchy, pistachio-topped cookies are a lovely, pastel shade of green - perfect for your "green theme" gathering, or St. Pat's Day, of course.
Preheat the oven to 300°F. Lightly grease two round 8" or 9" cake pans. If you worry about the shortbread possibly sticking in your particular pans, line them with parchment, and grease the parchment.
In a medium-sized bowl, beat together the butter, pistachio pudding mix, sugar, salt, and pistachio flavor, then beat in the flour. The mixture may seem a little dry at first; keep beating till it comes together. If it absolutely won't come together, dribble in up to 1 tablespoon of water, until it does. This is a stiff dough.
Divide the dough in half. Press each half into one of the prepared pans, smoothing the surface with your fingers, or with a mini rolling pin.
Use a fork to prick the dough all over; this allows any steam to escape, and prevents the shortbread from bubbling as it bakes. Divide the chopped pistachios between the two pans, spreading them evenly and gently pressing them down onto the surface of the dough.
Bake the shortbread until it's a deep golden brown around the edges, about 35 to 40 minutes.
Remove the pans from the oven, and immediately turn each shortbread round out onto a clean work surface.
Using a pizza wheel or sharp knife, cut each round into 12 wedges. (Do this while the shortbread is still warm; if you wait until it's cool, it won't cut easily.) Transfer the shortbread wedges to a rack to cool.
Store shortbread, well wrapped, for up to a week; freeze for longer storage. The flavor improves as the shortbread ages.
