Preheat oven to 350°F. Grease and flour three 6-inch round cake pans and set aside.
In a large bowl, whisk to combine dry ingredients together.
In a separate bowl, combine sour cream and milk.
In the bowl of a stand mixer beat butter until smooth. Add sugar and beat until pale and fluffy.
Add eggs and eggs yolks, one at a time, beating on low speed until incorporated. Add vanilla extract.
Alternating half the flour mixture and half milk mixture to the butter. Mix on low speed until milk is absorbed. Add remainder of ingredients and mix until just incoporated.
Pour batter into prepared cake pans. Bake for 38 to 40 minutes or until wooden pick inserted in centre comes out clean.
Cool cakes before levelling and decorating.
Notes
Vanilla Butter CakeFrom Style Sweet Ca (she's the best!)Fluffy Strawberry ButtercreamSee Kelsey's blog post here!