Preheat oven to 180°C.
Line 3 6-inch cake pans with round parchment paper. Grease and flour the sides. Shake out the excess flour.
In a medium sized bowl, beat butter using a hand mixer until it's creamy.
Next, add sugar, oil and vanilla, and beat till well combined. Scrape the sides and bottom of the bowl.
In a separate bowl, add flour, baking powder and salt and whisk to combine. Keep aside.
In another small bowl, measure the milk and keep aside.
Now, turn your hand mixer to medium speed, and gradually alternate adding the flour and milk in the prepared butter mixture. Start and end with flour! So basically, add a little flour, the a little milk, then flour, the milk, then flour. Don't panic: It's not tricky or difficult, just add a little at a time. Beat until each one is almost completely combined before adding the next.
Remember to scrape down the sides and bottom while doing the above step.
In a separate bowl, add the egg whites and using a hand mixer on high speed, beat until stiff peaks form.
Using a rubber spatula, gently fold the egg whites into your batter. Take care to scrape the sides and bottom of the bowl so that the ingredients are well combined and take care not to over mix.
Evenly divide cake batter into three portions. I weigh the whole batter and divide it into three portions by weight just so it is accurate.
Put one portion of the batter directly into a prepared cake pan. The other two portions should go into two separate bowls. Now it is time for you to add red food color gel. The quantity of the food color you add depends on the shade you want. All that matters is that you add more in one and less food color in the other, so that one portion looks significantly darker than the other. Bake at 180°C for 10-15 minutes for me until a toothpick inserted in the center of each cake layer comes out clean or with few crumbs. For best results, rotate your cake pans halfway through the baking to ensure even baking.
Remove cakes from oven and allow to cool for 15 minutes. Run a knife around the inside rim of each pan and invert each onto a cooling rack.
Allow to completely cool before covering with frosting.