Pre-heat oven to 350 degrees and line a 12-cavity cupcake tin with cupcake papers.
Place strawberries in a food processor or blender and process until pureed.
In a medium bowl, mix together flour, baking powder, and salt.
In a separate small bowl, mix together milk, vanilla, and ⅓ C of the strawberry puree.
In the bowl of a stand mixer or in a large bowl with a hand mixer, cream butter on medium-high speed until it's light and fluffy, 2-3 minutes. Gradually add sugar and continue to beat until well-combined and fluffy. Add the egg and egg whites one by one, mixing on medium speed after each addition.
With the mixture on low, add half the flour mixture and mix until just blended. Add milk/strawberry mixture and mix until just blended. Continue with the rest of the flour, mixing until just combined, taking care not to over-mix. If you want your cupcakes to be a bit more red, add food coloring here, too.
Divide the batter evenly among the prepared cupcake tin.
Bake for 22-25 minutes, until a toothpick inserted into the center comes out clean. Let cupcakes cool in the pan for a few minutes before removing to wire racks to cool completely.
Once completely cooled, frost cupcakes with strawberry frosting. I used a Wilton 1A tip to frost mine.