10 tablespoons (145 grams) unsalted butter
1 1/4 cups (250 grams) granulated sugar
3/4 cup plus 2 tablespoons (80 grams) unsweetened cocoa powder, natural or Dutch-process
1/4 rounded teaspoon kosher salt, use slightly less if using fine sea or table salt
1 teaspoon vanilla extract
2 large cold eggs
1/2 cup (65 grams) all-purpose flour
2/3 cup (75 grams) chopped walnuts or pecans, optional
Add enough water to a medium saucepan so that it is 1 to 2 inches deep. Heat water until barely simmering. Combine butter, sugar, cocoa powder, and the salt in a medium heat-safe bowl. Rest the bowl over simmering water (if the bottom of the bowl touches the water, remove a little water).
Stir mixture occasionally until the butter has melted and the mixture is quite warm. Don’t worry if it looks gritty; it will become smooth once you add the eggs and flour. Remove the bowl from heat and set aside for 3 to 5 minutes until it is only warm, not hot.
Stir in the vanilla with a wooden spoon or spatula. Then, add eggs, one at a time, stirring vigorously after each one.
When the batter looks thick, shiny and well blended, add the flour and stir until fully incorporated, then beat with the wooden spoon or spatula for 40 to 50 strokes. (The batter will be thick). Beat vigorously here. You want to see the brownie batter pulling away from the sides of the bowl (if you do not have the strength to do this by hand, use a hand mixer). Stir in nuts, if using. Spread evenly in lined pa
Bake 20 to 25 minutes or until a toothpick can be inserted into the center and come out almost clean (you want it to be a little moist with batter). Note: Some have found they need to bake an extra 10 minutes, so keep an eye on the doneness of the brownies and use the toothpick test as your guide.
Cool completely then remove from pan. For the cleanest lines when cutting, place into the freezer for 20 to 30 minutes to firm up. Cut into 16 squares.