---
source: https://www.youtube.com/watch?v=V0ki4Il9Npc
serves: 4
cook time: 20 minutes
total time: 45 minutes
---

Preheat oven to 450°F. Prepare a #10-inch cast iron skillet{}.

In a #10-inch cast iron skillet{} over medium heat, melt and brown @unsalted butter{1%stick (113g)}. Bring to a boil, stirring constantly until the foaming subsides and milk solids toast to a nutty golden brown, about ~{4%minutes}. Scrape the brown butter into a #bowl{} and place over an #ice bath{} to cool until thickened but still soft. Whisk in @heavy cream{1%Tbsp}.

In a #medium bowl{}, whisk together @all-purpose flour{100%g}, @Diamond Crystal kosher salt{1%tsp}, and @baking soda{0.5%tsp}. Set aside.

In a #large bowl{}, whisk together the cooled brown butter and @dark brown sugar{75%g}. Whisk in whole large @egg{1%large}, @egg yolks{4%large}, and @vanilla extract{1.5%tsp} until smooth. Whisk in the flour mixture until smooth, then fold in @dark chocolate{140%g} (finely chopped).

In a separate clean #mixing bowl{}, beat @egg whites{4%large} with a #hand mixer{} on medium-high until foamy. Add @cream of tartar{0.25%tsp}, then gradually stream in @granulated sugar{75%g}, beating until medium peaks form.

Gently fold one-third of the whipped egg whites into the cookie dough base to lighten it, then gently fold in the remaining egg whites until just incorporated with no visible streaks. Scrape the batter into the prepared #10-inch cast iron skillet{} and smooth the top.

Bake at 450°F for 18 to ~{20%minutes} until puffed and golden with set edges and a soft, medium-rare center. Serve immediately while warm straight from the skillet.