Preheat the oven to 350 degrees fahrenheit.
Grease and line muffin tins
In a large bowl, whisk together the non-dairy milk and vinegar. Let stand for about 5 minutes.
Add the sugar, oil, and vanilla extract, and whisk together until the mixture becomes frothy.
Sift together the flour, cornstarch, baking soda, baking powder, and salt.
Add the dry ingredients to the wet ingredients and whisk together until the flour mixture disappears.
Divide the batter evenly between the 3 pans (I used a kitchen scale to do this) and bake for 16 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Cool the pans on wire racks for about 15 minutes. Then turn the cakes out of the pans onto the wire racks and cool completely before frosting.