Cocoa Ribbon Cookies

Let 1 stick unsalted butter sit at room temperature until softened. Meanwhile, coarsely chop 3 ounces dark chocolate (heaping 1/2 cup) and place in a small microwave-safe bowl.

Finely grate the zest from 5 medium oranges (about 2 tablespoons) into the bowl of a food processor fitted with the blade attachment. Add 1 cup granulated sugar and 1/2 teaspoon kosher salt. Pulse in short bursts until the sugar turns a bright yellow color and is very fragrant, about 30 seconds.

Add the butter and 1/4 cup extra-virgin olive oil. Process until the butter becomes fluffy and loose in consistency, 2 to 3 minutes. Add 1/4 cup sour cream and pulse until combined, about 10 (1-second) pulses.

Transfer 1 cup of the batter to a medium bowl. Add 1 cup of the all-purpose flour to this batter and mix with a flexible spatula until an orange dough forms.

Melt the chocolate in the microwave on high in 15-second intervals, stirring between each. Add the chocolate to the remaining batter in the food processor. Sift 2 tablespoons Dutch-processed cocoa powder over the batter. Pulse, stopping and scraping down the sides of the food processor as needed, until combined and a glossy and smooth batter forms, about 10 (1-second) pulses.

Add the remaining 1 cup all-purpose flour to the food processor and pulse until combined and the dough forms a ball around the blade, about 15 (1-second) pulses.

Place the chocolate dough in between 2 sheets of parchment paper. Using a rolling pin, roll the dough out into a rough 8 1/2 x 11 1/2-inch rectangle about 1/2-inch thick.

Remove the top layer of parchment paper and reserve for baking. Evenly dollop the orange dough over the chocolate batter. Using a spatula or your hands, spread the orange dough into an even layer. Grasping the parchment, slide the cookie dough sheet onto a baking sheet or large plate. Refrigerate until slightly hardened but still malleable enough to push your finger into and make a dent, 8 to 10 minutes.

Slide the dough sheet, still on the parchment, onto a work surface and position with a longer side closer to you. Make 3 parallel cuts, spaced evenly apart, across the dough so that you are left with 4 (2 1/8 x 11 1/2-inch) strips. Slide a long offset spatula or metal bench scrape under the strips to help loosen them, then stack the strips on top of each other. Gently press down on the stack to ensure all the layers are sticking to each other.

Freeze until fully hardened, about 30 minutes. Meanwhile, arrange a rack in the middle of the oven and heat the oven to 350°F. Line a baking sheet with the reserved parchment paper.

Using a knife or bench scraper, trim off the rough edges for the stack of dough. (Don’t throw away the scraps: press them together to form a marbled cookie dough, chill it, slice it, and bake at the end.)

Working quickly to keep the dough as cold as possible, cut the dough crosswise into 1/2-inch-thick slices. If some cookie dough layers fall apart as you’re slicing, simply push them back together. Arrange the cookies on the baking sheet, spacing them at least 1 inch apart.

Bake until the cookies are light golden-brown on the bottom, 12 to 15 minutes. Let cool for 5 minutes on the baking sheet, then transfer to a wire rack and let cool completely before making the toppings.

Finely grate the zest from 1/4 medium orange (about 1/8 packed teaspoon) into a small bowl. Add 1 tablespoon granulated sugar and rub the zest into the sugar with your fingers until the sugar is fragrant and yellow in color.

Coarsely chop 4 ounces dark chocolate (about 3/4 cup). Transfer heaping 1/2 cup to a small microwave-safe bowl. Heat in the microwave on high in 15-second intervals, stirring between each, until melted and smooth. Add the remaining chocolate and stir until all the chocolate is melted and smooth.

Dip each cookie halfway into the melted chocolate and return to the baking sheet. Freeze until the chocolate is almost set, 2 to 3 minutes. Immediately sprinkle the chocolate-covered side with the orange sugar and flaky salt. Let sit until the chocolate is completely set, about 10 minutes more.