makes one 8- by 8-inch pan; adapted from Alice Medrich, Bittersweet
Preheat oven to 325°F. Place butter, sugar, cocoa and salt in a stainless steel bowl and set over or in a pan of simmering water. Stir occasionally until butter is melted and sugar is dissolved, about 5 minutes. Remove the bowl from the frying pan and set aside until the mixture is warm, no longer hot.
Line an 8-inch square baking pan with foil or parchment paper or spray pan with baking spray, leaving a slight overhang on two opposite sides.
Stir in the vanilla then add the eggs, one at a time, stirring vigorously after each one. Add the flour and stir until it is mixed in, then beat vigorously for about a minute. Spread evenly in the prepared pan.
Bake until a toothpick inserted into the center emerges slightly moist with batter, about 25–30 minutes. Let cool completely on a rack.
To preserve the crust, keep brownies loosely covered at room temperature.