In a small saucepan, add the raspberries and ¼ cup of sugar. Heat on medium high and gently mash the raspberries. Cook until the juices begin to thicken. Strain out all of the seeds through a fine mesh strainer and chill the thickened raspberry syrup.

In a mixing bowl, mix together the egg whites and remaining sugar. Hold the mixer over a small saucepan with simmering water as though the mixing bowl were the top of a double boiler.

Whisk the egg white mixture until the sugar dissolves completely.

Remove and beat the egg whites until they are stiff, glossy, and the mixing bowl is cool to the touch.

Beat in the butter one tablespoon at a time, mixing well between each addition before adding more butter.

Add the salt and vanilla.

Continue beating the buttercream and slowly drizzle in the raspberry syrup and the champagne. Keep beating for a few minutes. The mixture may seem to separate, but it will come together if you keep beating.