Preheat your oven to 350°F (175°C). Lightly grease an 8-inch square baking pan or line it with parchment for easy removal.

In a large bowl, whisk together 1 1/2 cups flour, 1 cup sugar, 1/4 cup unsweetened cocoa powder, 1 teaspoon baking soda, and 1/2 teaspoon salt until no streaks remain.

Make a well in the center. Add 1/3 cup neutral oil, 1 tablespoon vanilla, and 1 tablespoon vinegar.

Pour in 1 cup cold water (or cooled coffee). Whisk gently, starting in the center and working outward, until the batter looks smooth. Don’t overmix; a few tiny lumps are fine.

Scrape the batter into the prepared pan. Tap the pan once on the counter to pop big bubbles.

Bake for 28–34 minutes, or until the center springs back and a toothpick comes out with a few moist crumbs.

Cool in the pan for 10 minutes. Run a knife around the edges, then transfer to a rack to cool completely if frosting. For a quick finish, dust with powdered sugar while warm.

Optional glaze: Whisk 1 cup powdered sugar, 2 tablespoons cocoa, 1–2 tablespoons water or dairy-free milk, and 1/2 teaspoon vanilla until pourable. Drizzle over the cooled cake.