Set your oven to 350°F and prepare two 8x2 cake pans
Set your mixer with the paddle attachment or use a large bowl and a hand mixer
In a separate bowl, combine the flour, baking soda, baking powder, and salt, give it a quick whisk, then set aside.
Cream together the butter, oil, sugar, and sour cream. Mix on medium to high speed until the mix looks light and fluffy. Turn your mixer off, using a rubber spatula, scrape the bottom and sides of the bowl to make sure all ingredients are well combined.
Add the eggs and the egg yolk and mix for 2 minutes. Scrape the bottom and sides of the bowl as necessary. Add the vanilla and mix until all ingredients are fully incorporated.
Turn your speed to low and add the buttermilk and the flour alternating. Start and end with the flour. Beat until the ingredients are incorporated. Do not over mix.
Divide the batter into two prepared 8" cake pans.
Bake at 350°F for about 20 minutes. Time will depend on your oven.
Once you take your cakes out of the oven, let them rest on the cake pan for about two to five minutes, then transfer them to a cooling rack.
Once the cake has cooled down, add three scoops of the vanilla buttercream and spread evenly.
spread one cup of fresh berries on top of the buttercream then top with the next cake. repeat this process as many times as needed. ( for multiple layer cakes)
Finish the top layer with 3 scoops of buttercream. spread it evenly then add the fresh berries and mint sprigs to your liking.