Step 1

Preheat the oven to 350°F/177°C. Grease and flour three 8-inch round baking pans. Line the bottom of the pans with parchment paper and set aside.

Step 2

In a medium bowl, whisk the flour, baking powder, baking soda, and salt. Set aside.

Step 3

In a large bowl, using a hand-held mixer or stand mixer fitted with the paddle attachment, beat the butter and sugar on medium-high speed until smooth and creamy. Scrape down the sides of the bowl as needed.

Step 4

Add the oil and beat for 1 minute.

Step 5

Beat in eggs, one at a time, until combined. Scrape down the sides of the bowl and beat in the vanilla and sour cream until mixed.

Step 6

With the mixer on low speed, in three parts, alternate adding the dry ingredients and milk to the batter, beginning and ending with the dry ingredients. Beat until just combined.

Step 7

Evenly divide the batter between the three prepared pans and bake for 28-32 minutes, or until a toothpick inserted in the center comes out clean.

Step 8

Allow the cakes to cool in the pans for 15 minutes then transfer them to a cooling rack to cool completely before frosting.

Step 9

In a large bowl, using a hand-held mixer or stand mixer fitted with the paddle attachment, beat the butter on medium-high speed for 2 minutes.

Step 10

With the mixer on low speed, slowly add in the powdered sugar and beat until completely incorporated.

Step 11

Add the vanilla and mix to combine. Add the heavy cream, one tablespoon at a time until desired consistency is achieved. Beat the buttercream on medium-high speed for 5 minutes.

Step 12

Once the cakes have cooled, use a large serrated knife to slice a thin layer off the top of each cake to level.

Step 13

Place a layer of cake onto a cake turntable, cake stand, or serving dish. Evenly spread 1/4 of the buttercream over the cake. Top with a second layer and repeat with another 1/4 of the buttercream. Add the final cake layer.

Step 14

Spread a thin crumb coat over the entire cake and refrigerate for 30 minutes (or freeze for 5 minutes).

Step 15

Frost the cake with the remaining buttercream.