Preheat oven to 350 degrees F. Grease the bottom and sides of a 9x13-inch pan. Set aside.
In a medium bowl, combine sifted cake flour, baking powder, baking soda and salt. Set aside.
If making buttermilk, combine ingredients in a large glass measuring cup or small bowl and set aside to allow coagulation. I used whole milk and vinegar to make buttermilk for this cake.
Using a stand up or hand mixer, cream butter and sugar on high speed for 3-5 minutes until light and fluffy. Scrape down sides.
Add eggs and vanilla extract to the buttermillk in the measuring cup and stir together.
With mixer on low, alternate the flour mixture and buttermilk mixture until all ingredients are just combined. Do not over-mix the batter. Make sure to scrape down the sides during the process.
Fold strawberry puree into batter.
Pour cake batter into prepared pan. Bake for 30 - 40 minutes. Adjust time slightly according to your oven. My oven time was 37 minutes. Toothpick should come out mostly clean when checked in the center. Allow to cool completely before decorating.
Careful not to over-bake as the cake will continue to cook for 10 minutes on a cooling rack.
Puree fresh, ripe strawberries in a food processor, or blender.
In a medium sauce pan, reduce puree on the stove by heating on low-medium heat until reduced to about ½ cup. Usually, about 30 minutes. More time depending on your pan and the juiciness of the berries. Do not add sugar to the puree.
Allow to cool completely and store in an airtight container. Refrgerate if not using right away. Make sure to bring the puree back up to room temperature before adding to batter.
STRAWBERRY SIMPLE SYRUP
In a small sauce pan, combine chopped strawberries, water and sugar over medium-high heat and bring to a boil
As the mixture begins to boil, reduce heat to low and simmer for 5 minutes.
Cool to room temperature then strain. Store in refrigerator in an air tight container for up to 2 weeks.
In a large bowl, use a stand-up or hand mixer to cream butter. Add powdered sugar and combine completely.
Add milk, vanilla extract and salt. ** Replace vanilla extract with strawberry simple syrup if you want more berry flavor in the butttercream.
Beat for 3 to 5 minutes until smooth and creamy and you reach your desired consistency.
The Prep and Cooking times are for the entire process before decorating.