Preheat oven to 350F. Grease and flour three 8" cake rounds and line with parchment.
In a medium bowl, whisk flour, baking powder, baking soda and salt until well combined. Set aside.
Using a stand mixer fitted with a paddle attachment, cream butter and sugar on med-high until well combined (about 3mins). Add oil and beat another 2 mins until pale and fluffy.
Reduce speed and add eggs one at a time fully incorporating after each addition.
Add vanilla, vinegar, cocoa powder, and enough red color gel to reach your desired color. I used a little more than half of a 0.75oz bottle of Americolor Super Red.
Alternate adding flour mixture and buttermilk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition.
Bake for 25-30mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack.
Red Velvet Crumble (optional):
Preheat oven to 350F and line a baking sheet with parchment. Add enough color gel to the melted butter so that it's a deep red color.
Place cake mix into a medium bowl. Add some or the butter and stir with a spatula. Add more butter until the cake mix starts to clump. Do not add too much!! It's easier to add liquid if it's too dry, but if you add too much butter you have to start over.
Spread on a parchment lined baking sheet and bake for approx. 10 mins. Cool completely. Break crumble apart if needed.
Cream Cheese Frosting:
Using a stand mixer or hand mixer beat butter until pale and creamy.
Reduce speed to low. Add powdered sugar 1 cup at a time and mix on low until well blended. Increase speed to medium and beat for 3 minutes. Add vanilla and continue to beat on medium for 1 minute.
Slowly add chilled cream cheese one cube at a time (about 1 tablespoon at a time). Beat well until blended and ensure no lumps of cream cheese remain.
If needed, add cornstarch or meringue powder 1 tablespoon at a time to stiffen the frosting (I didn't but this is an option).
Run mixer on low for a couple of minutes to remove any air bubbles.
Place one layer of cake onto a serving plate or cake stand. Top with about 1 cup frosting and spread evenly. Repeat with next layer.
Place final cake layer on top and crumb coat the cake. Add 1 cup of buttercream to the very top and smooth until it hangs over the sides. Do a swirl on the top with a large offset spatula and then use an icing smoother to smooth the sides and create a lip on the top with the frosting.
Sprinkle some red velvet crumble around the top if desired.