1 cup (2 sticks) unsalted butter, room temperature
9 ounces bittersweet chocolate, reserve 2 tablespoons for sprinkling (You can also use milk chocolate)
¾ teaspoon fine sea salt or table salt
¾ teaspoon baking soda
2 ¼ cups all-purpose flour, plus more for work surface
1 teaspoon pure vanilla extract
4 large egg yolks, room temperature
¾ cup granulated sugar
¾ cup packed dark-brown sugar
1 large egg, lightly beaten
INSTRUCTIONS
In a large bowl, cream together butter and both sugars on medium-high speed until light and fluffy, about 3 minutes.
Beat in egg yolks and mix until combined.
With hand-held mixer off, add in vanilla. Set aside.
In a large bowl, whisk together flour, baking soda, and salt.
With the mixer on low, add flour mixture to butter mixture; mix until just combined. Scrape down sides of bowl and mix to combine.
Divide dough into three equal portions. Wrap each portion with plastic wrap and transfer to refrigerator; let chill for 30 minutes. Meanwhile, coarsely chop chocolate into thin shards. Set aside.
Unwrap one portion of chilled dough and place on a lightly floured work surface.
Sprinkle with half the chocolate and top of a second portion of chilled dough.
Sprinkle with remaining chocolate and top with remaining portion of dough. Gently flatten with rolling pin.
Prepare a 7-inch cast iron skillet with baking spray. Carefully move cookie down to skillet.
Bake until cookie is set, 30-36 minutes, at 350 degrees F. Remove from oven and allow to cool just slightly for about 3 minutes.
Add ice cream and sprinkle with remaining chopped chocolate.