Preheat the oven to 325°F. Line a glass 8x8x2” glass baking dish with foil, pressing firmly into the pan and leaving a 2” overhang. (A metal pan can also be used, preheat the oven to 350°F.) Spray the foil with nonstick spray.

Melt the butter in a small saucepan over low heat. Let cool a few minutes.

Meanwhile, measure the sugar, cocoa and salt into a medium bowl and whisk to blend. Gradually pour in the butter, whisking to blend. Whisk in the vanilla. Add the eggs one at a time, beating vigorously to blend after each addition. Add the flour, and using a rubber spatula or large spoon, stir just until combined (do not overmix). Scrape the batter into the prepared pan, smoothing the top.

Bake until the brownie feels just firm to the touch and a toothpick inserted into the center comes out with a few moist crumbs attached, about 40-50 minutes.

Place the pan on a wire rack and let the brownie cool completely. Using the foil, lift the brownie from the pan and transfer to a cutting board. Cut into 16 squares. (Can be prepared 3 days ahead. Wrap tightly and store at room temperature.)