To make the cake:

Cup of Yum
1. Preheat oven to 350° F. Grease the edges of three 8" x 2" round cake pans. Dust with flour and tap out the excess. Line the bottom of each pan with a circle of parchment paper.
2. In a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium-high speed until fluffy and pale, about 4 to 5 minutes. Lower the speed to medium and add the egg whites gradually, mixing until fully incorporated.
3. In a medium bowl, sift the flour, baking powder and salt. Whisk vanilla extract and vanilla paste (or contents of vanilla bean) into buttermilk. Pour one third of the dry ingredients into the butter mixture and mix until incorporated. Add half of the buttermilk, then repeat with the remaining dry ingredients and buttermilk, beginning and ending with dry ingredients. Mix until just incorporated.
4. Divide the batter evenly between the prepared pans. Smooth with small offset spatula, and bake for 30 minutes, or until a toothpick inserted in the middle of the cake comes clean.
5. Cool the cakes in the pans for 10 minutes, then run a knife around the edges, turn the cakes out onto a wire rack and peel off the parchment paper. Let cool completely.

To make the strawberry frosting:

1. Puree the strawberries in a food processor. Strain the puree through a fine mesh sieve placed over a bowl to remove the seeds. In an electric mixer fitted with the paddle attachment, combine butter and half of the sugar. Beat on low speed until well blended. Add the other half of the sugar and two tablespoons of strawberry puree, mixing until combined. Increase speed to medium and add additional puree, a tablespoon at a time, until desired color and flavor is reached (I used all of the puree). Add vanilla and beat on high for about 30 seconds to lighten the frosting.

To assemble the cake:

1. Place one cake layer on a cake stand, plate or cake board. Spread and smooth 3/4 cup frosting, using a small offset spatula. Repeat with second cake layer. Place the third cake layer on top and frost the top and sides of the cake with the remaining strawberry frosting. Refrigerate for at least 30 minutes and serve.