• Preheat your oven to 160°C (320°F) with the fan setting on. If your oven doesn’t have a fan function, see note 1 for adjustments. Prepare two 8-inch round cake pans by greasing or lining them with parchment paper. (Homemade cake release also works well.)
• In a medium bowl, sift together the flour, cornstarch, baking powder, and salt. Use a whisk or fork to mix everything thoroughly, then set aside.
• In a large mixing bowl, combine the softened butter, vegetable oil, granulated sugar, and brown sugar. Using an electric mixer—either a stand or hand mixer—beat the mixture for about 2 minutes until it becomes light, fluffy, and creamy.
• Add the eggs one at a time, mixing well between each addition (about 10–15 seconds per egg) to fully incorporate them into the batter.
• Next, mix in the sour cream and vanilla extract until fully combined. At this point, set your mixer aside—the rest of the batter will be mixed by hand.
• Add half of the dry ingredients to the wet mixture and gently fold it in with a spatula until just combined. Then pour in the milk and fold again until incorporated. Finally, add the remaining dry ingredients and fold gently, mixing only until no streaks of flour remain. Avoid overmixing to keep the cake light and tender (see note 3).
• Evenly divide the batter between the two prepared cake pans and smooth the tops. Bake in the preheated oven for 28–30 minutes, or until a toothpick inserted into the center comes out clean.
• Once baked, let the cakes cool in the pans for 15–20 minutes, then carefully turn them out onto a wire rack to cool completely before frosting.

Caramel Frosting

• In a large, heavy-bottomed saucepan, combine the butter, granulated sugar, evaporated milk, and salt. Place over medium heat and stir continuously until everything melts and comes to a gentle simmer. Once simmering, reduce the heat to low-medium.
• Let the mixture simmer and thicken slowly for about 1 hour, stirring every few minutes to prevent burning. Pay close attention as it begins to thicken and darken—this is when it’s most prone to scorching. When the caramel has thickened to a spreadable consistency and taken on a deep golden brown color, stir in the cream and vanilla extract. Mix until smooth and immediately pour the caramel into a heatproof bowl.
• Let the caramel cool for about 25 minutes before frosting the cake. You want it to remain slightly warm and pourable, as it sets quickly once applied. (If the caramel is too thick to work with, see note 4 for tips on loosening it.)

Assembly

• Once the cake layers have completely cooled, level the tops with a serrated knife to create flat, even surfaces.
• Place the first cake layer on your serving plate or cake stand. Spread a generous amount of warm caramel frosting on top and smooth it out with an offset spatula or knife.
• Place the second cake layer on top, then cover the top and sides of the cake with the remaining caramel frosting. If the frosting feels too soft or isn’t setting, refer to note 5 for troubleshooting.
• As the caramel begins to set, it will develop a shiny finish. For an ultra-smooth look, gently run a clean offset spatula or knife over the surface once the shine appears. Decorate however you like—add a drizzle of extra caramel, sprinkle with sea salt, or top with nuts—and enjoy your rich, decadent caramel cake!