Preheat your oven to 350°F (175°C).
Lightly grease your donut pan with cooking spray or oil.
In a large mixing bowl, combine the milk, egg, oil or melted butter, vanilla extract, and vinegar. Whisk until smooth.
In another bowl, whisk together the self-rising flour, baking soda, and sugar.
Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.
Gently fold in the mini chocolate chips.
Spoon the batter into the prepared donut pan, filling each cavity about 3/4 full.
Bake for 10-12 minutes, or until lightly golden and a toothpick comes out clean.
Cool the donuts in the pan for a few minutes before transferring them to a cooling rack.
