Preheat the oven to 160C (320F) and line the bottom and the sides of three 6” (15cm) round cake pans with parchment paper.
In a bowl, combine the flour, corn starch, baking powder, and salt. Set aside.
In a stand mixer fitted with a paddle attachment (or you can use a large mixing bowl and a hand mixer), add the butter and sugar. Beat on medium-high until pale and fluffy. Then, add the oil and beat until fully incorporated. Scrape the bottom and the sides of the bowl and beat 10 extra seconds.
Add the caramel and beat until you reach a homogenous consistency. Add one egg at a time and beat until fully incorporated and fluffy. Scrape the bottom and the sides of the bowl.
Add the dry ingredients in three parts alternating with the milk, starting and ending with the dry ingredients, while beating on low until a homogenous and silky consistency is reached. The pattern should look like this – dry/milk/dry/milk/dry.
Divide the batter evenly between the pans (around 300g per pan) and bake for around 30 minutes or until a toothpick inserted in the center comes out clean.
Remove from the oven and let cool down in the pans until safe to handle. Then, place the cakes onto a cooling rack to cool down completely.
If you want to assemble the cake the next day, wrap each cake layer in plastic wrap and refrigerate overnight.