Start by preheating your oven to 340°F (171°C). Grease an 8x8-inch (20x20 cm) square baking pan and line it with parchment paper, ensuring the paper hangs over the edges for easy removal once the brownies are baked.
In a heatproof bowl, place the dark chocolate and vegetable oil. Using a double boiler or the microwave in short bursts (stirring between each burst), melt the chocolate and oil until smooth and fully combined.
Once the chocolate mixture is melted, add the brown sugar, powdered sugar, milk, water, and vanilla extract. Whisk everything together until the mixture is smooth and well incorporated.
In a separate bowl, whisk together the all-purpose flour and cornstarch until fully combined. Gradually add this dry mixture to the wet ingredients, stirring constantly until the batter is smooth and free of lumps.
Stir in the red food coloring, mixing until the batter achieves a vibrant red hue. Make sure the color is evenly distributed throughout.
In a small bowl, combine the white vinegar and baking soda. Once it starts to fizz, quickly fold this mixture into the brownie batter, ensuring it is fully incorporated.
Pour the batter into the prepared pan and use a spatula to smooth the top. Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs attached.
Allow the brownies to cool completely in the pan before attempting to ice them.