Vanilla Cake
Preheat the oven to 350F. Grease and flour a 9×13 inch baking pan, or line it with parchment paper.

In a bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a separate bowl, cream together the butter and sugar until fluffy, about 2 minutes.

Add the eggs, egg whites, and vanilla extract. Beat until combined, about 30-60 seconds.

Scrape down the sides of the bowl.

Beat in the sour cream, then half of the flour mixture.

Beat in the milk, followed by the remaining flour mixture. Don’t overmix.

Pour the batter into the prepared pan and bake for 30-35 minutes, or until a toothpick comes out clean.

Let the cake cool completely before frosting.

Strawberry Buttercream Frosting
Pulse the strawberries in a food processor or blender until smooth.

Strain the puree to remove seeds. You should have about 1 1/4 to 1 1/2 cups.

Heat the puree in a saucepan over low-medium heat until it gently boils, stirring occasionally.

Boil for 10-15 minutes until thick and dark red-pink. You should have about 1/3 cup left. Cool.

In a bowl, beat the butter until fluffy.

On low speed, beat in 2 cups of powdered sugar.

Add the cold reduced strawberry puree, vanilla, and salt. Beat on low.

Beat in an additional 2 cups of powdered sugar.

On medium speed, beat for 30 seconds.

Add extra powdered sugar and cream as needed for consistency.

Frost the cooled cake.