Special equipment: An 8-inch square baking pan

Position a rack in the lower third of the oven and preheat the oven to 325 F. Line the bottom and sides of the baking pan with parchment paper or foil, leaving an overhang on two opposite sides.

Melt the butter in a heavy bottom sauce pan. Turn off burner and whisk in cocoa, then the sugar and salt. Stir in the vanilla with a wooden spoon. Add the 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 you cannot see it any longer, then beat vigorously for 40 strokes with the wooden spoon or a rubber spatula. Stir in the nuts, if using. Spread evenly in the lined pan.

Bake until a toothpick plunged into the center emerges slightly moist with batter, 20 to 25 minutes. The sides do not need to pull away from the pan. Let cool completely on a rack. Lift up the ends of the parchment or foil liner, and transfer the brownies to a cutting board. Cut into small squares.

Chocolate note: Any unsweetened natural or Dutch-process cocoa powder works well here. Natural cocoa produces brownies with more flavor complexity and lots of tart, fruity notes. I think it's more exciting. Dutch-process cocoa results in a darker brownie with a mellower, old-fashioned chocolate pudding flavor, pleasantly reminiscent of childhood.

Pecan note: The brownies are even more delicious if you roast the pecans 5-8 minutes before adding them to the batter.