Separately mix wet ingredients EXCEPT vinegar. Add liquid to dry stir until smooth.
Add vinegar and chocolate chips and mix to combine. Do not over mix, there will be streaks of vinegar.
Spray a 9" round baking pan with cooking spray or line muffin tins with paper liners. Pour in the batter into the prepared pan. Bake for 25-30 minutes or until a skewer comes out clean. Muffins will take ~20 minutes.
Makes 1, 9" cake or 18 cupcakes.
Unless it's a special occasion, I usually skip frosting this cake because the chocolate chips add just the right amount of extra sweetness.