1. Start whipping the egg whites on medium high. Bring to a soft peak, then add 1/3 cup sugar.
2. While the egg whites are whipping, place 1-1/3 cups of sugar and the water in a pot and boil until it reaches 240°, the soft ball stage. If you do not have a thermometer, the soft ball stage is reached when a small amount of the sugar/water mixture is dropped into a cup of ice water and it forms a soft pliable ball. Take off the heat and let the bubbles subside.
3. In a nice steady stream pour the cooked sugar into the egg whites. Whip for another 10 minutes or so until the bowl feels cool to the touch.
4. Add the Plugrá Butter in pieces and whip until it is light in color and fluffy.
5. Fold raspberry puree into 2/3 of the finished buttercream frosting.
6. Fold mango puree into remaining buttercream frosting.