First things first, set your oven to 350°F (175°C) so it’s nice and hot when you’re ready to bake. Grab two 9-inch round cake pans—give them a good grease with butter or cooking spray, then dust them lightly with flour, or you can just line them with parchment paper if you prefer.

In a big bowl, sift together the flour, cornstarch, baking powder, and salt. This makes sure everything’s evenly combined and fluffy. Set that bowl aside for now.

In another large bowl, beat the softened butter and sugar with an electric mixer until the mixture is light and fluffy—this usually takes about 3 to 4 minutes, so don’t rush it.

Add the eggs one at a time, making sure to beat well after each addition so everything blends smoothly. Then stir in the vanilla extract for that lovely flavor.

Now, pour in the oil slowly, then start adding the dry ingredients and milk alternately—start with some dry stuff, then milk, then dry again, and so on—until everything is just combined. Be careful not to overmix here, or your cake might turn out tough.

Divide your batter evenly between the two pans, smoothing out the tops with a spatula. Pop them into the oven and bake for about 30 to 35 minutes. You’ll know it’s done when a toothpick poked into the center comes out clean.

Once baked, let the cakes rest in the pans for about 10 minutes to set up. Then, carefully flip them out onto a cooling rack and let them cool completely before frosting.

For the frosting, beat room temperature butter until creamy. Gradually add in the powdered sugar and cocoa powder, mixing on low speed. Pour in the heavy cream and vanilla extract, then stir in the melted and cooled chocolate. Beat everything together on medium speed until it’s smooth and fluffy.

Place one cake layer on your serving plate, spread a generous amount of that delicious chocolate buttercream over the top, then add the second layer. Use the remaining frosting to cover the whole cake, smoothing it out with an offset spatula or a knife.