If using frozen raspberries, thaw for 20 minutes. If using fresh raspberries, rinse them.
Rinse the mint, pluck the leaves from the stems, and finely chop most of them; save a few whole leaves for garnish.
Mix the 2 tablespoons granulated sugar with the chopped mint and let steep for 2-3 minutes.
In a mixing bowl, combine the 400 g quark, 2 tablespoons sugar, vanilla sugar, lemon juice, and 4 tablespoons mint syrup. Stir until smooth.
Using a hand mixer, whip the 100 g cream until stiff peaks form. In the last 30 seconds of whipping, sprinkle in the cream stabilizer and continue whipping to incorporate.
Gently fold the whipped cream into the quark mixture with a spatula.
Divide the quark-cream mixture evenly among 4 serving glasses.
Drizzle the remaining 4 tablespoons of mint syrup over the tops (about 1 tablespoon per glass).
Top each with the raspberries and sprinkle with the mint sugar mixture.
Garnish each with a mint leaf and refrigerate until ready to serve.