In a metal mixing bowl combine the egg whites, salt, and sugar and stir until combined. Place over a double boiler and hit the egg white/sugar mixture until the sugar is completely dissolved and the temperature reaches 180°.
Using a whip attachment and a mixing bowl, with the egg whites/sugar mixture on high until it doubles in volume and becomes thick and shiny. Whip until cool.
In a large bowl, using an electric mixer on a slow speed (#2 - #4) add pieces a bother bit at a time, until butter is incorporated. Remember to scrape down side of bowl, add meringue into butter.
Add the vanilla and beat to incorporate. Heat on high for one minute to ensure all the butter is totally combined with the whipped egg whites and sugar mixture.
Use immediately or place in an airtight container and chill. Be sure to rework the buttercream before using.
Add a ½ cup of melted 70% chocolate to the buttercream and blend to combine. The Buttercream might curdle slightly, so continue to beat until it becomes smooth again.
Add ½ cup raspberry preserves, and whip until completely incorporated.