In a large mixing bowl, combine the softened butter and granulated sugar. Using a hand mixer set to medium speed, cream the mixture for about 1 to 2 minutes until it becomes light, fluffy, and pale in color.

Add in the vanilla extract and freshly grated orange zest. Beat briefly until the zest and vanilla are evenly distributed throughout the butter mixture.

Gradually add the all-purpose flour and kosher salt. Beat on low speed just until the flour disappears and a soft dough begins to form. Gently fold in the chopped cranberries and pistachios, ensuring they are evenly mixed without overworking the dough.

Divide the dough in half and shape each portion into a 6-inch log. Wrap each log tightly in plastic wrap to hold its shape. Refrigerate the dough for at least 1 hour, or leave it to chill overnight for easier slicing and better flavor development.

When ready to bake, preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats to prevent sticking.

Unwrap the chilled dough and slice into 1/2-inch thick rounds. Arrange the slices on the prepared baking sheets, spacing them about 2 inches apart to allow for slight spreading. Bake in the preheated oven for 10 to 12 minutes, rotating the trays halfway through for even coloring. The edges should turn a light golden hue while the centers remain pale.

Remove the baking sheets from the oven and let the cookies cool for 5 minutes on the sheets before transferring them to a wire rack to cool completely.

Once fully cooled, store the shortbread cookies in an airtight container. They will maintain their crisp, buttery texture for up to 2 weeks, making them perfect for gifting or keeping on hand for a sweet treat.