Preheat your oven to 160°C (320°F) with the fan setting on (refer to note 1 if your oven doesn’t have a fan function), and grease or line two 8-inch cake pans (homemade cake release works well).

In a medium bowl, sift together the flour, cornstarch, baking powder, and salt. Use a whisk or fork to mix thoroughly until the dry ingredients are well combined, then set aside.

In a large mixing bowl, combine the butter, vegetable oil, granulated sugar, and light brown sugar. Using an electric mixer—either hand-held or a stand mixer (see note 2)—cream the mixture for about 2 minutes until it becomes light, fluffy, and creamy.

Add the eggs one at a time, mixing well after each addition for about 10 to 15 seconds between each.

Next, mix in the sour cream and vanilla extract until fully incorporated. At this point, put the mixer aside as the rest of the batter will be mixed by hand.

Add half of the dry ingredient mixture to the wet ingredients and gently fold in with a spatula until just combined. Pour in the milk and fold again until just combined. Finally, add the remaining dry ingredients and fold gently until no streaks remain. Be careful not to overmix (see note 3).

Divide the batter evenly between the two prepared pans and bake for 28 to 30 minutes, or until a toothpick inserted into the center of the cakes comes out clean.

After baking, allow the cakes to cool in their pans for 15–20 minutes, then carefully turn them out onto a wire rack to cool completely before frosting with the caramel.

Place a large saucepan over medium heat and add the butter, granulated sugar, evaporated milk, and salt. Stir continuously as everything melts together and comes to a simmer. Once simmering, reduce the heat to low-medium.

Let the caramel slowly thicken for about an hour, stirring every few minutes to avoid burning. As it thickens, it will require more frequent attention to prevent scorching. Once the caramel reaches a deep golden brown and thick consistency (refer to video if available), stir in the cream and vanilla extract until smooth. Immediately pour the finished caramel into a heat-safe container.

Allow the caramel to cool for about 25 minutes before frosting the cake. It should still be slightly warm and pourable when used, as it sets up quickly when applied (see note 4 if it becomes too thick to spread).

Once the cake layers are completely cool, level the tops with a serrated knife to create flat, even layers.

Place the first cake layer on a cake stand or serving plate and generously spread caramel frosting over the top using an offset spatula or a knife.

Position the second cake layer on top and cover both the top and sides with the remaining caramel frosting (see note 5 if the caramel is too thin and hasn’t set properly). As the caramel begins to set, it will take on a glossy shine. For a super-smooth finish, lightly run an offset spatula or knife over the shiny surface. Decorate as desired and enjoy!