Preheat your oven to 350°F (175°C) and line muffin tin with paper liners.

In a medium bowl, whisk together the cake flour, baking powder, baking soda, and salt.

In a large mixing bowl, beat the softened unsalted butter with granulated sugar until pale and fluffy, about 3-5 minutes.

Incorporate the large egg and add the egg whites one at a time, mixing well after each addition.

Mix buttermilk, fresh strawberry puree, and vanilla extract; add to flour mixture in three batches, stirring gently.

Fold in diced strawberries gently with a spatula.

Divide the batter evenly into the lined muffin cups, filling each about 3/4 full.

Bake for 20-23 minutes, or until a toothpick comes out clean.

Remove from the oven and let cool in the tin for 5 minutes, then transfer to a wire rack.

For the frosting, reduce strawberry puree in a saucepan until thick, then cool. Beat softened butters and gradually mix in powdered sugar and cooled puree until smooth.

Pipe the strawberry buttercream frosting onto the cooled cupcakes and garnish with whole strawberries.