Combine flour, sugar, baking powder, and salt via shifting. In another bowl combine the pureed strawberries, lemon zest, milk, and vanilla. Set both of these aside while you cream together the butter and sugar until fluffy-like. Add the egg and egg whites one at a time until fully incorporated. Now take turns adding the flour mixture and the strawberry mixture slowly until everything is fully mixed together. Scoop into your cupcakes liners, making sure they are evenly filled.