Preheat your oven to 350 degrees. Line 2 cupcake trays with cupcake liners. Set aside.

In a stand mixer fitted with the paddle attachment, beat the butter, strawberry Jell-O, and granulated sugar for about 2 to 3 minutes, until light and fluffy. Scrape the bowl, and then beat for 2 more minutes.

With the mixer on medium speed, gradually add the egg whites and the whole egg, making sure to scrape down the sides of the bowl between each addition.

Add the sour cream and vanilla. Mix for another 2 minutes on medium speed. Scrape down the bottom and sides of the bowl. If it looks a little curdled, that’s okay, it’s normal. Once you add the flour it will smooth out.

In a medium sized bowl, whisk together the cake flour, baking powder, and salt. Set aside.

With the mixer on low speed, alternately add the flour mixture and the buttermilk, starting and ending with the flour mixture. Mix until combined. Don’t over mix. Use a rubber spatula to scrape the bottom and make sure you’ve gotten all of it.

Fill the batter with a piping bag or a ziplock bag, and fill the prepped cupcake liners ¾ full. Bake for 18-22 minutes or until a toothpick is inserted with little to no crumbs left.

Once they are done baking, let them cool for 20 minutes. Make the marshmallow buttercream.

In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and cream cheese on medium speed for about 2 minutes.

Scrape down the sides with a rubber spatula, and with the mixer on low speed, gradually add the sifted powdered sugar, one cup at a time, mixing in between each addition.

Add the marshmallow cream, followed by the vanilla and salt. Beat on medium speed until incorporated.

Turn the mixer to medium speed and beat for an additional 3 to 5 minutes.

Before piping onto your cupcakes, use your rubber spatula and beat the frosting by hand for a couple minutes to remove the air pockets.