Whisk whole-wheat flour, all-purpose flour, fennel seeds, baking soda and salt in a medium bowl. Beat butter, sugar and orange zest in a mixing bowl with an electric mixer on medium-high speed until light and fluffy, scraping the sides of the bowl halfway through. Add egg whites and orange extract and beat until combined. Scrape down the sides and beat for another minute or so. Reduce speed to low and slowly add the flour mixture, beating until a soft, sticky dough forms.Advertisement
Place half the dough on a large piece of plastic wrap and shape into a 10-inch log (it's OK if it's not perfectly round). Repeat with the remaining dough. Wrap and freeze until just firm, about 45 minutes. Reroll the logs to make them rounder and return to the freezer until very firm, at least 1 hour more (or up to 3 months).
To bake cookies: Preheat oven to 350 degrees F. Line a baking sheet with parchment paper or a silicone baking mat.
Remove one log of dough at a time from the freezer and let stand at room temperature for 5 minutes. Place about half the pistachios on a clean cutting board. Unwrap the dough and roll in the pistachios, pressing to adhere. Slice the dough into 1/2-inch-thick rounds, turning the log a quarter turn after each slice to help keep the cookies round. If your cookies aren't as round as you want them to be, shape the dough with your fingers. Place 1/2 inch apart on the prepared baking sheet.
Bake the cookies until light brown on the bottom, 12 to 14 minutes. Transfer to a wire rack to cool. Repeat with the remaining dough and pistachios.
To make ahead: Freeze dough (Steps 1-2) for up to 1 month; store cookies airtight at room temperature for up to 3 days.
Equipment: Parchment paper or silicone baking mat
1/2 starch, 1/2 other carb, 1/2 fat