Push the strawberry puree through a metal sieve to remove the seeds (this is optional for the cupcake batter).
Add the strawberry puree to a medium saucepan over medium heat. Stir gently as the puree comes to a gentle boil. Boil for about 10-15 minutes while stirring, until the puree has reduced to about ⅓ of its original volume - ¼ cup. Cool fully.
Preheat the oven to 350F degrees and line muffin pans with muffin papers. You'll end up with about 18 cupcakes total.
In a medium bowl whisk together the cake flour, baking soda, baking powder and salt.
In a large bowl beat the butter and sugar until fluffy (about 3 minutes). Beat in the egg and egg white 1 at a time.
In a liquid measuring cup, whisk together ¼ cup of reduced strawberry puree, the vanilla extract, and buttermilk.
Beat about ⅓ of the flour mixture into the butter mixture, alternating with about ⅓ of the buttermilk mixture. Repeat the process until all the flour mixture and buttermilk mixture are added.
Gently fold the chopped strawberries into the cupcake batter using a rubber spatula.
Spoon the batter into the prepared muffin pan, filling each muffin paper about ⅔ to ¾ full.
Bake in the preheated oven for 16-19 minutes, or until the tops are set and an inserted toothpick comes out clean.