Preheat oven to 350 and line cupcake pan with paper wrappers.
In a large bowl, beat the butter, Jell-O powder, and sugar until well combined. Set aside.
Separate eggs into two bowls, reserving the whites for later. Add all four yolks to the Jell-O mixture and mix on medium speed until fully combined. Set aside again.
In a medium bowl, sift your cake flour. This is very important! Sift the flour into a bowl, then carefully spoon it into measuring cups. Measure 2 3/4 cups of sifted flour into a large bowl, and add in the baking powder.
Add half of the flour mixture to your Jell-O bowl, and mix until combined. Add half the milk and mix again, then repeat until both bowls are combined.
Make your strawberry puree by pulsing 12-15 hulled strawberries in a blender of food processor with 1/2 Tbsp of sugar. Add to the batter.
Add vanilla extract and mix well.
Whip the reserved egg whites until soft peaks form, and then gently fold them into the batter.
Fill the cupcake wrappers to about 1/2" from the top and bake for 20 minutes, or until a toothpick inserted into the center of the cupcake comes out clean.
Allow cupcakes to cool fully on a baking rack before frosting.