Fudgy Dark Chocolate Brownies

Method

1. Heat the oven to 350°F with a rack in the middle. Line a 9-inch square pan with a parchment sling, leaving the paper hanging over two sides.
2. Melt the butter and chocolate together in a heatproof bowl set over a pot of barely simmering water, stirring until smooth, then take it off the heat and cool 5 minutes.
3. In a large bowl, whisk both sugars, the eggs, vanilla and kosher salt hard for 3 to 4 minutes, until pale and thick enough to fall off the whisk in a ribbon.
4. Whisk in the warm chocolate until glossy, then fold in the flour until no streaks remain. Scrape into the pan and smooth the top.
5. Bake 28 to 32 minutes, until the edges are set, the top is shiny and cracked, and a toothpick comes out with moist crumbs. Sprinkle with flaky salt, cool completely in the pan (about 1 hour), then lift out and cut with a hot knife.