Preheat the oven to 335º F/168º C — 350º F/177º C and prepare two 8-inch pans or three 6-inch cake pans with cake goop or another preferred pan release.
It is important to use warm ingredients so that everything incorporates correctly. Add the eggs to a bowl of warm water (in the shells) for 5 minutes, heat the milk in the microwave for 30 seconds, and leave the butter out for a few hours, or cut it into cubes and microwave for about 10 seconds.
Separate your eggs and egg yolks by cracking each egg on the table and using your thumbs to divide the shell into two pieces. Move the yolk back and forth and allow the whites to fall into a bowl.
Whisk together the eggs, egg yolks, milk, vanilla, and vegetable oil in a medium bowl and set it aside.
Place the cake flour, sugar, baking powder, baking soda, and salt into the bowl of a stand mixer with the paddle attachment. This can also be made with an electric hand mixer in a large mixing bowl.
Slowly add your softened butter in chunks and mix on medium speed until the batter resembles coarse sand.
Add ⅓ of your egg/milk mixture to the flour mixture while mixing on low speed until just moistened. This part is crucial, be careful not to add too much liquid.
Increase the mixer to medium speed (setting 5 on Kitchen Aid mixer) and whip for 2 minutes until it has thickened and lightened in color. It should look like soft-serve ice cream. If you do not let the batter mix fully, you will end up with short, crumbly cakes.
Scrape the bottom and sides of the bowl.
While mixing on low speed, slowly add in the rest of your wet ingredients to the fluffy cake batter, stopping to scrape the bowl one more time halfway through. Mix until the liquids are fully combined in the batter.
Divide the cake batter evenly between the prepared cake pans.
Bake for 30 minutes and then check your cakes. If they are still jiggly in the center bake for another 5 to 8 minutes. If they are almost set, bake for another 5 minutes or until the center springs back when you touch it, or a toothpick comes out clean. Bake time can vary depending on the size and shape of the cake pans you use.
Let the cakes cool in the pan for 15 minutes or until the pan is just barely warm. Then, turn them out onto a wire rack to finish cooling.
Wrap them in plastic wrap and freeze if you're decorating the next day. Or if you're decorating the same day, I like to put mine into the freezer (unwrapped) and on the cooling rack to flash chill for one hour so I can begin frosting.