Preheat your oven to 350°F (175°C). Grease and line two 8-inch (20cm) cake pans with baking paper.
In a bowl, combine the milk and vinegar, and let it sit for 5 minutes until it slightly curdles.
Add both types of sugar, vegetable oil, and vanilla extract to the bowl. Mix with a whisk until the sugars are dissolved.
Sift in the dry ingredients (cinnamon, corn starch, baking powder, baking soda, flour, and salt) and mix until smooth.
Divide the cake batter evenly between the two prepared cake pans.
Bake for 25-30 minutes or until the cakes are firm to the touch and a toothpick inserted in the center comes out clean.
Allow the cakes to cool completely on a wire rack. Trim a very thin layer off the top of each sponge cake before assembling.