Pour the frozen raspberries into a strainer, let them thaw and drain. If desired, drizzle with a few drops of raspberry brandy. Beat the egg yolks with the sugar and vanilla sugar until a foam forms. Add a pinch of salt to the egg whites and beat them until stiff peaks form. Gently incorporate them into the egg yolks. Butter the soufflé molds. Divide the raspberries among the molds and pour in the egg mixture. Slide into a preheated oven at 325°F, on the second rack from the bottom, and bake for about 15 minutes.