Step 1

Position a rack in the middle of the oven and preheat to 350 degrees. Spray a 9-by-13-inch pan with nonstick cooking oil spray. Line the bottom with a piece of parchment paper long enough to have an overhang over two opposite sides of the pan.

Step 2

In a medium saucepan over medium heat, melt the butter. Remove from the heat and add the cocoa powder, stirring to combine. Let cool slightly.

Step 3

In a large bowl, whisk the eggs together, then add the sugars and the vanilla extract, stirring to combine. Add the cooled butter-chocolate mixture, then fold in the flour and salt until just combined; do not overmix. Spread the batter evenly in the pan, making sure the corners are filled.

Step 4

Bake for 40 to 45 minutes, or until a crust forms on the surface and a toothpick inserted into the center comes out mostly clean. Transfer to a wire rack and let cool completely in the pan, about 2 hours. Using the parchment, lift the brownie out of the pan (if you meet any resistance, gently run a butter knife around the edges.)Slice into 24 pieces (or however many you like) and serve.