Preheat oven to 350 F.
Line 24 count cupcake pan with liners.
CAKE:
In large bowl, sift together the cake flour, baking powder and salt. Set aside.
Cream butter until pale yellow.
Add sugar and continue to cream butter mixture until light and fluffy
Add in egg whites two at a time, mix well after each addition.
Combine milk, water and vanilla.
With mixer on low add flour mixture one spoonful at a time alternating with the milk mixture and ending with the flour mixture. increase mixer to medium and mix until just combined, scraping the sides and bottom of bowl as needed.
Fill cupcake cavities 3/4 of the ways full. Tap on counter 3 times to release air bubbles.
Bake 19-23 minutes or until toothpick inserted comes out clean.
Let cool completely
BUTTERCREAM:
Cream butter until light and fluffy.
Add vanilla bean seeds and continue to mix.
With mixer on low add powdered sugar one spoonful at a time, mix until combined and scrape sides and bottom of bowl as needed.
Add in the strawberry puree and continue mixing.
With mixer on medium/high slowly drizzle in the white chocolate.
Continue mixing until completely combined.
Add in the vanilla extract and mix until combined.
(if consistency is too soft, possibly from the cooled but warm white chocolate, place in refrigerator for 30 min to chill/stiffen the buttercream, not too much longer than that though, you don't want buttercream to get hard).
STRAWBERRY PUREE:
Place everything in medium sauce pan.
Mash strawberries as they begin to soften.
Bring to a boil and then bring down to a simmer.
Simmer until reduced by half stirring often, about 30-45 min.
Let cool completely.
ASSEMBLY:
Arrange cupcakes on cookie sheet.
Cut small hole in center of each cupcake that goes as deep as half way down.
Pour 1 tsp of strawberry puree in center of cupcakes and place cutout round back on top. It will not fit perfectly, thats ok because you will be frosting over the tops.
Pipe buttercream over tops of the cupcakes and add sprinkles if using them. (I used Ateco tip# 808 and SprinklePop mix “Romance”.
I put the sprinkles in a shallow dish and rolled just the bottom edge in the sprinkles.