1cup(226 g) unsalted butter, softened, but still cool
¾cup(150 g) granulated sugar
½cup(50 g) confectioners’ sugar
2large egg yolks, room temperature
⅓cup(56 g) semisweet chocolate, melted and slightly cooled
2teaspoonspure vanilla extract
Instructions
In a medium bowl, whisk together the flour, cocoa powder and salt. Set aside.
In the bowl of a stand mixer (or using a hand mixer), beat butter, granulated sugar and confectioners’ sugar together on medium speed until light and fluffy, about 2 minutes.
Add the egg yolks, melted chocolate and vanilla. Mix until well combined. Scrape down the bottom and sides of the bowl as needed.
Add the flour mixture and mix just until combined. The dough should be soft, but not sticky. If it’s sticky, place the bowl of dough in the refrigerator for 10 to 15 minutes.
Divide the dough in half. Roll each half into a 6-inch long about 2 inches in diameter. Wrap each log of dough in plastic wrap and chill in the refrigerator for 2 hours. I suggest rotating them after 30 minutes so they don't become flat on one side.
Adjust oven racks to the upper-middle and lower-middle positions. Preheat oven to 325℉. Line two baking sheets with parchment paper. Set aside.
Unwrap one of the dough logs and slice ¼-inch thin slices. After every slice, turn the log of dough slightly to avoid flattening one side of the log.
Place the rounds of dough 1 ½ inches apart on the prepared baking sheets. Bake at 325℉ for 14 minutes. Halfway through the baking time, rotate the pans 180 degrees and swap them top to bottom. Cool the cookies on the pan for a couple minutes, then transfer them to a wire cooling rack to cool completely.
Notes
Dutch process cocoa powder is preferred since it has a smoother chocolate flavor. If this recipe had baking soda, then natural unsweetened cocoa powder (non-alkalized) would be preferred to neutralize the acidity.Make ahead the dough and store in the refrigerator for up to 48 hours or in the freezer for up to 3 months.Store in an airtight container at room temperature for up to 1 week.Freeze baked cookies for up to 3 months.