Preheat over to 350 degrees.

Heavily coat 2- 9″ round baking pans with a non-stick spray like Baker’s Joy. Set aside.

Combine flour, cake flour, baking powder, baking soda & salt in a mixing bowl & whisk to sift. Set aside.

In the bowl of an electric mixer, whip together butter & granulated sugar using the paddle attachment.

Combine eggs & yolks into a measuring cup.

Pour in eggs, oil & vanilla into butter mixture & continue to beat.

Add in 1/3 of the flour mixture & mix until just combined.

Pour in 1/2 the buttermilk, mix.

Repeat the process again with the remaining flour & buttermilk, scraping down the sides of the bowl between mixing.

Divide the batter between the prepared cake pans.

Bake 25-30 minutes or until toothpick test is clean.

Cool in pans at least 10 minutes.

Run a knife around the edges to loosen from the pan.

Invert the cakes onto a wire rack & continue to cool.

After about 20 minutes of cooling, wrap each cake layer in plastic wrap to help the cakes retain their moisture. (especially if you live in a dry climate)

Chill the cakes in the refrigerator or freezer prior to decorating to make spreading the frosting easier.

Frost with chocolate buttercream frosting.

Store in an airtight container.