These cookies from the Persian tradition are a rather special gluten-free version of shortbread--just be sure to use powdered sugar that doesn't include a starch with gluten in it. The most classic version of the cookie is made with white rice flour, but I prefer to use whole-grain brown rice flour (now widely available; Bob's Red Mill is a common brand) because it gives a more melting texture with a little grit, like cornmeal. If you like a more intensely spiced cookie, use the full teaspoon of cardamom; the lesser amount offers a more nuanced flavor.
Serves 40 (serving size: 1 cookie)
1. Combine sugar, butter, and oil in the bowl of a stand mixer; beat at medium speed for 1 1/2 minutes or until well combined and pale. Add cardamom and egg yolk, beating until combined. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Gradually add flour and salt to butter mixture, beating just until combined. Divide dough into 2 equal portions. Shape each portion into a 6-inch log. Wrap logs individually in plastic wrap; refrigerate 12 to 24 hours.
2. Preheat oven to 350°.
3. Cover 2 baking sheets with parchment paper. Remove dough logs from refrigerator. Cut each log into 20 slices; place slices 1 inch apart on baking sheets. (Pat slices together if they crumble.) Sprinkle with pistachios. Bake at 350° for 17 minutes or until edges begin to brown, rotating pans halfway through. Let stand 5 minutes; place cookies on a wire rack. Cool completely.