Crisp, buttery, and gorgeously swirled, these peppermint shortbread cookies are as festive as they are flavorful. A portion of the vanilla dough is flavored with peppermint oil for just the right amount of cool, minty flavor, then the two colors are twisted together in an eye-catching pattern. Don’t worry: The assembly process is easier than it looks (especially with the help of a scale). Once assembled, the log can be stashed in the refrigerator or freezer, so you’re only a few slices away from holiday cookies whenever you need them.
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To make the cookie dough: In the bowl of a stand mixer fitted with the flat beater attachment or working in a large bowl with an electric hand mixer, beat the butter, sugar, and salt until light and fluffy, about 2 to 5 minutes on medium speed, depending on the temperature of your butter.
Add the egg yolk and vanilla and beat until incorporated, stopping to scrape the sides of the bowl as needed.
Add the flour and mix on low until a crumbly dough forms.
Transfer the dough to a clean work surface and bring the dough together into one mass. Use a scale to divide the dough into two portions: 355g and 175g. (If you don’t have a scale, divide the dough into thirds and then combine two thirds to form the larger piece.) Transfer the larger piece to the work surface and round the dough into a smooth ball: This is the vanilla dough. Place the smaller piece of dough in the mixer bowl: This will become the peppermint dough.
To make the peppermint dough: In a very small microwave-safe bowl, stir together the packet of red food coloring, water, and peppermint oil. Microwave in 2-second intervals, stirring between each, until the food coloring is dissolved and the mixture is smooth.
Add all of the red mixture to the dough in the mixer bowl. Mix on low speed until the color is evenly distributed and the dough has come together.
To assemble: Working on a piece of parchment or on a clean, lightly floured surface, divide the vanilla dough into four pieces, about 88g each. Round each piece into a ball, then roll out into a log about 10" long. Divide the red dough into three pieces, about 58g each. Round each piece into a ball, then roll out into a log, about 10" long.
Use your hands to slightly flatten one log of vanilla dough to about 1 1/2" wide. Place a peppermint log on top of the flat vanilla log, then use your fingers to slightly flatten the peppermint log to the same width, about 1 1/2".
Repeat with the remaining logs of dough, alternating between vanilla and peppermint, until you have a stack of flattened logs.
Use your hands to gently roll the stack of flattened logs of dough to round the edges and form one large log about 10" long. Twist the ends of the large log in opposite directions to create a swirled effect.
To make a perfectly round log, place the log of dough on a sheet of parchment, then fold the parchment away from you to encase the dough. Use your nondominant hand to press a straight object (a ruler or a bench knife works well) between the dough and the work surface, then use your dominant hand to gently tug the parchment away from you. This should pull the dough so that it butts up against the straight object and makes a very smooth, symmetrical log. See this blog post, How to make round cookies, for a visual demonstration.
To finish: Spread the sparkling sugar on a piece of parchment in a 2"-wide strip about 10" long. Roll the dough log in the sugar to coat.
Wrap the sugar-coated log in plastic wrap or transfer to a Slice-and-Bake Cookie Dough Keeper. Cover and refrigerate until very firm, at least 2 hours and up to 4 days.
When ready to bake, preheat the oven to 350°F with racks in the upper and lower third. Line two baking sheets with parchment.
Remove the dough from the refrigerator, unwrap or remove from the Keeper, and slice into 1/4"-thick rounds. Rotate the log about 90° (a quarter turn) every three to four slices to maintain a neat circular shape. Transfer the slices to the parchment-lined baking sheets, spacing about 2" apart.
Bake the cookies for 15 to 20 minutes, rotating the sheets top to bottom and front to back halfway through, until the edges of the cookies are golden brown. Remove from the oven and let cool on the baking sheet for about 10 minutes before transferring to a wire rack to cool completely.
Storage information: Store leftover slice-and-bake cookies, well-wrapped, at room temperature for up to 1 week; freeze for longer storage.
Tips from our Bakers
Want to make this recipe gluten-free? For great results, substitute King Arthur Gluten-Free Measure for Measure Flour for the all-purpose flour in this recipe. Be sure to bake thoroughly; gluten-free baked goods often need a bit more time in the oven.
Liquid or gel food coloring can also be used to color the dough: Add it directly to the smaller portion of dough along with the peppermint oil in step six (omit the water), adjusting the quantity as needed.
