Preheat oven to 350ºF. Butter or grease a 9×9-inch baking pan, line with parchment paper, and then butter or grease the parchment. Set aside.
Combine red wine and two tablespoons of sugar in a small pot over high heat and bring to a boil. Cook, stirring occasionally, until reduced to ¼ cup. Set aside to cool.
Melt butter and chocolate in a large, heat-proof bowl set over a pot of simmering water, stirring occasionally with a spatula. When melted and fully combined, set aside to cool.
Whisk brown sugar, remaining cup of white sugar and eggs in a large bowl until sugar granules dissolve, about 1 minute. Whisk in cooled chocolate-butter mixture, then the red wine reduction and vanilla until the mixture is fully combined and has a glossy sheen.
Add flour, cocoa powder and salt all at once, and stir until just combined.
Pour into prepared pan and tap on your countertop so it spreads evenly into all four corners. Bake for 35–40 minutes, or until middle is set. Let cool at least 15 minutes before cutting into 16 squares.
