Step 1

Position a rack in the lower third of the oven and preheat to 325 degrees F. Line the bottom and sides of an 8-inch-square baking pan with parchment paper or foil coated with cooking spray, allowing it to slightly overhang opposite edges.

Step 2

Bring 1 inch water to a bare simmer in a medium saucepan. Combine chocolate and butter in a metal bowl large enough to rest in the pan without touching the water. Cook, stirring occasionally, until melted and smooth, about 5 minutes. Remove bowl from heat. Add sugar and salt and stir until combined. Let cool until barely lukewarm, 5 to 7 minutes.

Step 3

Add eggs one at a time, whisking briskly after each. Add flour and whisk briskly for 30 seconds to thicken the batter. Stir in nuts. Scrape the batter into the prepared pan and spread evenly.

Step 4

Bake until a toothpick inserted in the center emerges clean, 25 to 30 minutes. Let cool completely in the pan on a wire rack, about 1 1/2 hours. Lift the overhanging ends of paper or foil to remove from the pan. Cut into 16 brownies.