Serves: Makes 16 (2-inch) brownies
- ½ cup (1 stick) unsalted butter, cut into ½-inch pieces
- 4 ounces semisweet or bittersweet chocolate, finely chopped
- 2 ounces unsweetened chocolate, finely chopped
- 1 cup sugar
- 2 large eggs, at room temperature
- 1½ teaspoons pure vanilla extract
- ½ cup unbleached all-purpose flour
- Pinch of salt
- ½ cup chocolate chips or chunks (optional)
- ½ cup chopped nuts of your choice, toasted and cooled (optional)
Preheat the oven to 350°F and position an oven rack in the center. Line an 8-inch square cake pan with foil or parchment paper across the bottom and up two of the sides, then lightly coat with an oil spray.
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 until the chocolate is melted and smooth.
Remove 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. Whisk in the flour and salt. Continue to stir until the batter changes from dull and broken-looking to smooth and shiny, about 1 minute. Whisk in the chocolate chips and chopped nuts, if using.
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.
Run a thin knife or flexible spatula around the edges of the pan to loosen the brownies. Grasp the foil or parchment paper extending up the sides and pull gently upward. Set the brownies on a cutting surface and cut into 16 equal pieces. Since these are fudgy, keep a hot, wrung-out wet 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. Tightly wrap the remaining brownies in plastic or place in an airtight container. They will keep well at room temperature for 2 to 3 days or in the refrigerator for up to 5 days.