Preheat oven to 350°F/177°C. Grease and line two 8-inch heart shaped pans. Set aside.
To make the cake, beat the softened butter in a bowl using a wooden spoon.
Add in the eggs one at a time beating each addition.
Pour the water into the egg mixture then add in the cake mix and continue beating until mixture is well blended and smooth.
Tint the cake mixture with light pink food color as desired then pour and divide the cake mixture in two prepared pans. Bake in the pre heated oven for 25-30 minutes or until baked. Cool and set aside.
Prepare buttercream by placing the egg whites and 1 cup of sugar in a mixer bowl over simmering hot water. Make sure the simmering water does not touch the bottom of the bowl. Stir until the sugar has been dissolved. Remove the bowl from heat.
Transfer the bowl in a stand mixer and beat the mixture at high speed for 1 minute then gradually add the remaining ¼ cup sugar. Beat again for another 2 minutes. Lower speed to medium and continue beating until the mixture is not warm to touch or until the mixing bowl is cool to the touch.
Add in the butter 1 tablespoon at a time. Beat for 4-5 minutes, add in the vanilla extract and continue beating or until everything is smooth and incorporated. Use meringue immediately or cover with wet towel or cling wrap.
Divide the buttercream mixture into two bowls and tint both mixtures with light and dark pink respectively.
Place the dark hue pink buttercream on piping bag using a rosette tip. Then set aside.
To assemble the cake, place one baked heart cake on a serving dish or tray. Dollop and spread on top and sides of the first layer cake the frosting using the light-colored buttercream. Do the same procedure using the second baked heart cake.
Once the whole cake has been frosted with light buttercream, pipe rosette flowers on top of cake using the prepared dark pink buttercream on a piping bag. Make sure to cover the entire cake top with rosettes. Serve