Ingredients

• 1 stick (4 ounces) unsalted butter, cut into ½-inch pieces
• 4 ounces semisweet or bittersweet chocolate (up to 64 percent cacao), finely chopped
• 2 ounces unsweetened chocolate, finely chopped
• 1 cup (7 ounces) sugar
• 2 large eggs, at room temperature
• 1½ teaspoons pure vanilla extract
• ½ cup (2½ ounces) unbleached all-purpose flour
• Pinch of salt
• ½ cup (about 3¾ ounces) chocolate chips or chunks (optional)
• ½ cup (2 ounces) chopped nuts, toasted and cooled completely (optional)

Equipment

8-inch Square Cake Pan, Parchment Paper, Double Boiler, Silicone or Rubber Spatula, Whisk, Cooling Rack, Thin Knife or Flexible Spatula, Chef’s Knife

Procedure

1. Preheat the oven to 350ºF and position an oven rack in the center. Line the pan with foil or parchment paper across the bottom and up two of the sides, then lightly coat with unflavored oil or high-heat canola-oil spray.
2. Bring 2 inches of water to a boil in the bottom of a double boiler. Place the butter, semisweet chocolate, and unsweetened chocolate in the top of the double boiler (off the heat). Turn off the heat, then set the butter and chocolate over the steaming water. Stir occasionally with the spatula until the chocolate is melted and the mixture is smooth.
3. Remove the chocolate mixture from the heat and whisk in the sugar. Whisk in the eggs, one at a time, stirring well to incorporate each before adding the next. Stir in the vanilla extract. Whisk in the flour and salt. Continue to stir until the mixture changes from dull and broken-looking to smooth and shiny, about 1 minute. Whisk in the chocolate chips and chopped nuts, if using.
4. Scrape the batter into the prepared pan and spread evenly. Bake for 35 to 40 minutes, until a skewer inserted into the center of the brownies comes out with a few moist crumbs clinging to it (do not overbake). Transfer to a rack and cool completely.
5. Run a thin knife or flexible spatula around the edges of the pan to loosen the brownies. To remove the brownies from the pan, grasp the foil or parchment paper extending up the sides and pull gently upward. Set the brownies on a cutting surface and use a chef&$146;s knife to cut into 16 equal pieces. Since these are fudgy, it’s a good idea to keep a hot, wrung-out towel nearby so you can wipe the knife clean between slices. You could also serve the brownies right out of the pan, if you like, pressing a piece of plastic wrap against any cut surfaces and across the top to keep them fresh.