We used these brownies with our Mint Parfait, but they can be crumbled as a garnish over any sundae or served warm, topped with a scoop of ice cream.
Heat oven to 350 degrees. Butter an 8-inch-square baking pan; line with buttered parchment paper. Bring a small saucepan of water to a boil; turn off heat. Combine butter and chocolate in a small, heatproof bowl; set over the pan of water, stirring occasionally, until melted.
Whisk eggs in a large bowl, and add salt, sugars, and vanilla. Stir to combine. Stir in melted chocolate mixture. Sift in flour, and fold until combined. Pour batter into prepared pan; spread evenly. Transfer pan to the oven, and bake until top is shiny and batter is moderately firm, about 25 minutes. Let cool before cutting and removing from pan; serve.