Preheat oven to 350F and grease and flour three 6" cake rounds, line with parchment.
In a medium bowl, whisk flour, baking powder, and salt. Set aside.
Using a stand mixer fitted with the paddle attachment, beat butter until smooth. Add sugar and beat on med-high until pale and fluffy (2-3mins).
Reduce speed and add egg whites one at a time, fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and milk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition.
Add a small amount of pink color gel using a toothpick. Mix to incorporate but try not to overmix.
Spread batter evenly into prepared pans. Smooth the tops with a spatula.
Bake for approx. 25 mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack to cool completely.
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a hot water bath on the stove and whisk constantly until the mixture is hot and no longer grainy to the touch (approx. 3mins).
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth. Add vanilla and continue to whip until smooth.**
Place one layer of cake on a cake stand or serving plate. Top with approximately 2/3 cup of frosting and spread evenly creating a bit of a lip on the edge. Fill with 1 Tbsp raspberry jam.
Repeat with remaining layers and apply a thin coat of frosting all over the cake. Chill for 20mins.
Frost and smooth the sides and pipe ruffle dollops on top using a 1M tip. Chill for 20mins.
Place candy hearts randomly around the cake -- starting with the darker hearts at the bottom and working your way up to the top and lighter colors.
Sprinkle top of cake with a variety of pink and white sprinkles if desired.
* Ensure there is NO trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease free or your meringue won't stiffen.** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth.