2 ¼ cups flour ¾ tsp. baking soda ¾ tsp. kosher salt 16 tbsp. unsalted butter, softened ¾ cup packed dark brown sugar ¾ cup sugar 1 tsp. vanilla extract 4 egg yolks 9 oz. bittersweet chocolate, roughly chopped
1. Heat oven to 375°. Whisk together flour, baking soda, and salt in a bowl; set aside. Combine butter, both sugars, and vanilla in a large bowl; beat on medium-high speed with a hand mixer until smooth and fluffy, about 3 minutes. Add yolks two at a time, beating after each addition; add dry ingredients; beat on low speed until just combined. Transfer dough to a work surface; divide into 3 equal pieces. Flatten each into a 4″ x 6″ rectangle; wrap in plastic wrap. Chill for 30 minutes.
2. Place one dough rectangle on a floured work surface; sprinkle with half the chocolate. Top with another rectangle, sprinkle with remaining chocolate, and cover with last rectangle. Using a floured rolling pin, flatten rectangles into a 9″ x 6″ x 1 ½″ rectangle. Using a 2″ round cutter, cut out cookies; transfer to parchment paper—lined baking sheets, spaced 3″ apart. Gather scraps, reroll into a 1 ½″-thick disk; cut out more cookies. Bake, rotating baking sheets halfway through cooking, until lightly browned and set, about 15 minutes.