In a medium bowl, whisk together the sifted all-purpose flour, baking powder, and salt. Set aside.

In a large bowl, cream the softened unsalted butter and granulated sugar together using an electric mixer on medium-high speed until light and fluffy, about 3-4 minutes. Scrape down the sides of the bowl as needed. This process incorporates air, which is crucial for a tender cookie texture.

Add the large egg, orange zest, and vanilla extract to the creamed butter and sugar mixture. Beat on medium speed until well combined, about 1 minute. Then, add the orange juice and mix until just incorporated.

Gradually add the dry ingredients (flour mixture) to the wet ingredients in three additions, mixing on low speed until just combined after each addition. Be careful not to overmix, as this can develop the gluten in the flour and result in tougher cookies.

Gently fold in the roughly chopped pistachios using a spatula until evenly distributed throughout the dough. Ensure you don't overmix at this stage.

Cover the bowl with plastic wrap and refrigerate the dough for at least 30 minutes (or up to 2 days). Chilling the dough makes it easier to handle and prevents the cookies from spreading too much during baking, ensuring they maintain their shape and soft texture.

Preheat your oven to 180°C (350°F). Line two baking sheets with parchment paper or silicone baking mats. This prevents sticking and ensures even baking.

Place the powdered sugar in a shallow bowl. Roll tablespoon-sized portions of the chilled dough into balls, about 2.5cm (1 inch) in diameter. Ensure the balls are firm and compact.

Gently roll each dough ball in the powdered sugar, coating it completely. This coating will create the signature 'snowy' appearance after baking.

Place the coated dough balls onto the prepared baking sheets, spacing them about 5cm (2 inches) apart to allow for slight spreading. You should be able to fit about 12 cookies per sheet.

Bake for 10-12 minutes, or until the edges are lightly golden and the centers are set but still appear soft. The cookies will continue to cook slightly on the baking sheet after removal from the oven. Do not overbake if you desire a soft cookie.

Let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely. This allows them to firm up enough to be moved without breaking.

Once completely cooled, you can optionally roll the cookies in additional powdered sugar for an extra snowy effect, if desired. Store in an airtight container at room temperature for up to 5 days.