Best Cocoa Brownies

Position an oven rack in the lower third and preheat to 325 degrees Fahrenheit. Line an 8-by-8-inch baking pan with parchment paper, leaving overhang on two sides for easy removal.

Place the butter, sugar, cocoa powder, and salt in a medium heatproof bowl. Set the bowl over a skillet of gently simmering water and stir occasionally until the butter melts and the mixture is smooth and warm. Alternatively, melt in the microwave in short bursts.

Allow the mixture to cool until it feels warm but not hot. Stir in the vanilla extract. Add the eggs one at a time, stirring vigorously after each addition until the batter turns thick and glossy.

Add the flour and stir until just combined, then beat the batter vigorously with a wooden spoon or spatula for about 40 strokes to develop structure. Fold in the nuts if using, then spread evenly into the prepared pan.

Bake for 20 to 25 minutes, checking with a toothpick inserted in the center. The brownies are done when the toothpick emerges with a few moist crumbs attached but is not wet with raw batter.

Let the brownies cool completely in the pan on a wire rack. For the cleanest cuts, refrigerate briefly before slicing. Lift out using the parchment overhang and cut into 16 squares.