Preheat oven to 350°F (175°C). Grease both 9-inch pans, line the bottoms with parchment rounds, then grease the parchment too. Set aside.
In a large bowl, sift together the flour, cocoa powder, baking soda, and salt. Add the granulated sugar and whisk until fully combined.
In a separate bowl, whisk the vegetable oil, eggs, and buttermilk until smooth. Add the red gel food coloring, vanilla extract, and white vinegar. Whisk again until the color is fully even.
Pour the wet mixture into the dry ingredients. Mix on low speed just until no dry flour remains, scraping the bowl once. Stop as soon as the batter is smooth.
Split the batter evenly between the two prepared pans. Bake for 28 to 32 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.
Let the layers rest in the pans for 10 minutes. Run a knife around the edge, then turn the cakes out onto a wire rack. Cool fully, about 1 hour.
Beat the softened cream cheese and butter together until completely smooth, about 2 minutes. Add the powdered sugar one cup at a time, mixing on low. Beat in the vanilla and a pinch of salt.
Trim any dome off the layers with a serrated knife. Set the first layer on your plate, spread frosting over the top, then add the second layer. Frost the top and sides.