Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Line a standard-size cupcake pan with liners, and set aside.
In the bowl of a stand mixer (or a large mixing bowl with a hand mixer), beat the butter and sugar until light and fluffy, about 2-3 minutes. Add the egg whites one at a time, mixing after each addition. Add the vanilla extract, and mix to combine.
In a medium mixing bowl, whisk together the cake flour, powdered strawberries, baking powder, baking soda, and salt. With the mixer on low speed, gradually alternate adding the dry ingredients with the sour cream and milk. After all the ingredients are added, beat on medium for 15 seconds. Gently fold in diced strawberries.
Using a large cookie scoop (#20 or 3.5 tablespoons), fill each liner with the cupcake batter. Place in the oven and bake for 18-22 minutes or until the centers are set. Use a toothpick or cake tester to ensure they are done. Remove from the oven and allow to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
Meanwhile, to make the frosting, in the bowl of a stand mixer fitted with the whisk attachment (or a large mixing bowl using a hand mixer and the whisk attachment), beat the butter until smooth and creamy, about 1 minute. Add the powdered strawberries and turn the mixer to low speed. Gradually add the powdered sugar along with the strawberry puree, white chocolate, whole milk, vanilla extract, and salt. Increase the speed to high and beat for 3 minutes until fluffy. Chill in the refrigerator for 15 minutes before using.
Using a pastry bag fitted with a large piping tip, pipe the frosting onto the cooled cupcakes. Top with a fresh strawberry, if desired.
For the Puree
Use ⅓ cup of chopped strawberries and blend in a blender on high until smooth. If you want to remove the seeds, pour through a fine mesh sieve.
Cook and reduce the strawberry puree by placing it in a small saucepan over medium-high heat and bringing it to a simmer while stirring.
Once at a simmer, reduce the heat to low and stir frequently until the desired thickness is reached, up to 20 minutes. Stir frequently to prevent sticking.
Let the puree cool. Use it in this recipe, and for any remainder, refrigerate for up to 2 days or freeze for up to 6 months.
Notes
I'm partnering with Ghirardelli to bring you today’s recipe.To STORE Strawberry Cupcakes, keep them at room temperature in an airtight container for up to 2 days. Avoid refrigerating them, as the cold air can dry them out. If necessary, let them come to room temperature before serving.To FREEZE unfrosted cupcakes, let them cool completely, wrap them tightly in plastic wrap, and place them in airtight bags. They’ll last 3-4 months. When ready to serve, defrost at room temperature, unwrap, and frost before enjoying.