Preheat oven to 375 degrees and line cupcake pan with cupcake liners
In a medium sized bowl, combine powdered sugar and flour and set aside.
In stand-mixer, combine egg whites, cream of tartar, vanilla and salt. Mix well.
With mixer on high, beat in sugar, about 1 Tablespoon at a time, adding more only once the previous tablespoon has been dissolved (As you add the sugar, you should be able to hear the faint sound of the granules scraping against the metal bowl. Once you no longer hear this, the sugar has been dissolved). Do NOT scrape the sides of the bowl as you are doing this, just keep beating.
Beat until stiff peaks form*
Using a rubber spatula, gently fold in your sugar/flour mix, about 1/2 cup at a time. Do not overdo this step, fold only until the flour mixture is combined with the egg whites mixture.
Fill cupcake liners to the top and bake on 375 for 12 minutes.
Allow them to cool in the pan for about 5 minutes and remove from cupcake pan. Before cupcakes have cooled completely, cut about a 2 inch square hole in the center of the cupcake. Set the removed centers in a medium bowl, which you will use for the filling in the next step. Likewise, tear two cupcakes into small pieces and place them in the bowl as well.
Bring 1 cup water to a boil.
In the bowl with the cupcakes pieces, combine hot water, strawberry Jello mix, and frozen strawberries.
Combine all ingredients, chopping the strawberries into small pieces as they soften. Mix well.
Using a spoon, pour the filling into the hollowed out cupcakes, filling them to the top of the cups (It is very unlikely that you will use all of the filling mix).
Place cupcakes in the freezer for 15-30 minutes to chill before topping with whipped cream.
Whipped Cream Topping
In your stand mixer, combine heavy whipping cream, vanilla, and powdered sugar.
Starting on medium speed, gradually increase mixer speed to high and stir until desired consistency is reached (stiff peaks).
Remove cupcakes from freezer and pipe whipped cream on top. Top with blueberries or other fruit if desired.
*Stiff peaks are formed when you can dip a rubber spatula in to the mix and pull it straight back out and the peak/tip that is formed doesn't fold over at all.