Preheat your oven to 350 °F (175 °C) and line two muffin tins with a total of 16 cupcake liners.
In a large mixing bowl, stir together the milk and the vinegar. Let it sit for 5 minutes. Then stir in the oil, brown sugar, granulated sugar, and the vanilla extract.
In a medium mixing bowl, stir together flour, cocoa powder, baking soda, baking powder and the salt. Add this to the wet mixture and stir just until combined. Do not over mix! The batter will be almost as thin as water. Don't worry!
Fill the liners a little more than halfway full and bake for 16-18 minutes or until a toothpick inserted in the middle comes out clean or with some moist crumbs (but not raw batter). They will be very, very soft but will firm up as they cool.
Let them cool for 5 minutes, then turn out onto a wire rack to cool completely.