Preheat the oven to 350ºF and prepare three 6-inch or two 8-inch cake pans by spraying the sides with cooking spray and placing a wax or parchment paper circle into the bottom of each one. Measure the sifted cake flour by spooning into your measuring cup and leveling it, or simply sift the cake flour into a bowl on your kitchen scale to measure it. Place the cake flour into a medium sized bowl and add the cocoa powder, baking soda, and salt. Whisk together and set aside.
Cream the butter on high for two minutes, then add the vegetable oil and sugar. Cream together on medium-high until light and fluffy, about 2 minutes. Scrape down the bowl and paddle. Turn the mixer to low and add the eggs one at a time. Once the eggs are incorporated, add the vanilla and white vinegar and mix on low for another 30 seconds. Scrape down the bowl and paddle once more.
Mix the red food color gel into the buttermilk. With the mixer on low speed, alternate adding the flour mixture and buttermilk in three additions, beginning and ending with the flour mixture. Mix only until the ingredients start to come together, then whisk the batter by hand a few times to make sure there are no large lumps.
Pour the batter into prepared cake pans (no more than 2/3 full) and bake for 30-35 minutes, until a toothpick inserted comes out clean. Let the cakes cool in the pan for five minutes before carefully removing them and placing the cakes on a wire rack or cookie sheet. Allow the cakes to cool completely before assembling and frosting.