Preheat Oven to 350 F (176 C) and prepare three 6 inch cake pans with baking spray, then line the bottom with parchment paper.

In a medium bowl hand whisk together sifted flours, baking powder and salt. Set aside.

Using a hand mixer and a large bowl cream together softened butter and sugar. (You can also use a stand mixer with paddle attachment. You will just have to transfer the batter from to a separate bowl to use the stand mixer for whipping egg whites.)

Add vanilla, milk, and yogurt. Mix until incorporated.

Spoon in flour mixture and mix until a smooth batter is formed.

Next, add egg whites to bowl of stand mixer and whip in medium high for 6-8 minutes until stiff peaks form. ( You can whip you egg whites in the stand mixer, while you make the cake batter using a hand mixer in separate bowl to save time.)

Gently fold stiff egg whites into cake batter a third at a time until fully incorporated. (Do not stir.)

Measure and divide cake batter evenly into the three prepared pans.

Bake on the middle rack for 35-40 minutes until toothpick inserted into the center comes out clean or with small crumbs.

Let cakes cool completely on rack before removing from pans.