The Best Shortbread Cookies Four Ways

Ingredients

• 2 sticks butter unsalted at room temperature (8 ounces; 226 grams)
• 80 grams powdered sugar 
• 0.3 tsp sea salt fine
• 2 large egg yolk at room temperature
• 2 tsp vanilla extract pure
• 272 grams flour all-purpose
• 136 grams flour all-purpose
• 136 grams flour whole wheat
• 2 sticks butter unsalted at room temperature (8 ounces; 226 grams)
• 80 grams powdered sugar 
• 0.3 tsp sea salt fine
• 1  lemon zest grated
• 2 large egg yolk at room temperature
• 2 tsp vanilla extract pure
• 3 Tbsp wheat germ 
• 170 grams flour all-purpose
• 120 grams rye flour 
• 2 sticks butter unsalted at room temperature (8 ounces; 226 grams)
• 80 grams powdered sugar 
• 0.3 tsp sea salt fine
• 2 large egg yolk at room temperature
• 2 tsp vanilla extract pure
• 113 grams bittersweet chocolate mini finely chopped
• 170 grams flour all-purpose
• 120 grams rice flour 
• 2 sticks butter unsalted at room temperature (8 ounces; 226 grams)
• 80 grams powdered sugar 
• 0.3 tsp sea salt fine
• 1  orange zest finely grated
• 2 large egg yolk at room temperature
• 2 tsp vanilla extract pure
• 3 Tbsp flaxseeds toasted chopped

Equipment

• bowl
• baking sheet
• baking paper
• oven
• knife
• whisk
• wire rack
• blender
• hand mixer
• stand mixer

Directions

1. All of the shortbreads are made in the same manner using an electric mixer. If you’re making a shortbread with two kinds of flour, whisk the flours together.
2. Working in the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the butter, confectioners’ sugar, salt and zest, if using, together on medium speed until soft, creamy and homogenous, scraping the bowl as needed. One by one, beat in the yolks, followed by the vanilla.
3. Turn off the mixer, add the flour(s) all at once and mix on low speed only until incorporated. If you’ve got wheat germ, chocolate or flax seeds or nuts, mix in now.
4. Scrape the dough out onto the work surface and divide it in two; the dough will be soft and sticky. Put each piece on a sheet of parchment and cajole it into a log that’s 6 to 6 1⁄2 inches long, tightening the log with the paper and twisting the ends. Refrigerate the logs for at least 3 hours (overnight is better) or freeze them for 2 hours. (The logs can be frozen for up 2 months; slice when they're still frozen. You might need to add a minute to the oven time.)
5. When you're ready to bake: Center a rack in the oven and preheat it to 350°. Line a baking sheet with parchment paper or a baking mat.
6. Using a chef’s knife, cut each log into 1⁄2-inch-thick rounds.
7. Lay them out on the baking sheet, leaving about an inch between them.
8. Bake, rotating the cookie sheet after 10 minutes, for 21 to 23 minutes, or until the cookies are golden brown around the edges and set. The cookies will still be soft, so leave them on the sheet for 5 minutes before transferring them to a wire rack and allowing them to cool to room temperature.
9. DO AHEAD: The cookies can be packed in an airtight container and kept at room temperature for at least 5 days.