For the Topfen Filling: Beat whipping cream into stiff peaks and set aside. In a large mixing bowl, beat Topfen, lemon zest and juice, sugar and vanilla sugar until smooth. In a small saucepan, stir together agar-agar gelling powder and cold water and bring to a boil. Add 4-5 tablespoons of the Topfen mixture and bring to a boil again. Remove from heat and allow the mixture to cool for 5 minutes. (In the meantime get everything ready to assemble your cake because the filling will set quickly.) Whisk the agar-agar mixture into the remaining Topfen mixture. Fold in the whipped cream.
*For the Blueberry Swirl we’re basically making a jam that contains only a third of the sugar that regular jam has, thus 3:1 which is 3 parts fruit and 1 part sugar. If you don’t have this type of jam sugar, you could use regular blueberry jam for the swirl, perhaps cutting the sweetness by stirring in lemon juice and frozen blueberries.
Recipe inspired by essen & trinken.