Brown Butter Shortbread Cookies

Ingredients

• 5 ounces refined white sugar
• 
5 ounces unsalted butter
• 1/2 ounce malted milk powder, such as Carnation or Hoosier Hill Farm
• 1/4 ounce vanilla extract
• 1 teaspoon Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight

• 1/4 teaspoon baking soda
• 1/4 teaspoon baking powder
• 5 ounces all-purpose flour, such as Gold Medal

Directions

1. Put the sugar in a 10-inch stainless steel skillet. Set the skillet in a cold oven, then heat the oven to 350 degrees F (180 degrees C). While the sugar warms, make the brown butter as described next; around the time the butter is ready, the sugar should be lightly colored and smell caramelly. Tip the warm sugar into a 2-quart glass baking dish, or a similar dish, so it cools more quickly, and leave it until it is about 75 degrees F (24 degrees C). Once the brown butter has cooled completely, the sugar is ready to use, or you can seal it in an airtight container and store it indefinitely.
2. Melt the butter in a 2-quart stainless steel saucier over medium-low heat. Turn the heat up to medium and let it bubble, stirring with a heat-resistant spatula as it crackles and sputters. Nudge the heat up or down as needed so the milk solids do not burn before the water cooks off. Keep cooking, stirring, and scraping any browned bits from the pan until the butter turns golden yellow and the bubbling goes quiet, which means the water has cooked away. Scrape the butter and every browned bit into the bowl of a stand mixer, then let it cool until it is creamy, opaque, and not above 75 degrees F (24 degrees C). You can also refrigerate the brown butter for up to 3 weeks, then bring it back to that same temperature before using.
3. Once the brown butter is thick and creamy, add the cooled sugar, then the malted milk powder, the vanilla extract, the salt, the baking soda, and the baking powder. With the paddle attachment on the stand mixer, blend on low speed until everything comes together. Raise the speed to medium and beat until the mixture looks pale and fluffy. Turn the mixer back to low, add the flour, and mix just until the dough is evenly combined.
4. Use a flexible spatula to scrape the bowl and beater, checking that no dry or unmixed streaks are hiding, then press and fold the dough lightly against the bowl. Transfer it to a sheet of parchment paper and form it into a rough log about 12 inches long.
5. Fold the parchment over the dough. With a bench scraper, tuck the parchment beneath the log, then pull gently on the top layer of parchment to snug the dough into shape. Shift the scraper down a few inches and do the same thing again, continuing until the log is smooth and firm all the way around. Roll the dough up in the parchment, trim off the extra paper, and fasten it with a piece of tape. Tie the ends closed with twine. Chill the wrapped dough until it reaches about 40 degrees F (4 degrees C), which takes about 4 hours; the dough can also stay refrigerated for up to 1 week.
6. Set a rack in the lower-middle position, heat the oven to 350 degrees F (180 degrees C), and leave the chilled dough at room temperature for about 10 minutes so it softens slightly. With a sharp chef's knife, slice the log into rounds just shy of 1/2 inch thick. Place the cookies on a parchment-lined half-sheet pan and bake until they are golden brown, about 15 minutes. Let them cool completely before serving. In an airtight container, the shortbread will keep for several weeks at cool room temperature.