For the Philadelphia Strawberry Rhubarb Tart, place biscuits in a freezer bag, seal bag and crumble contents completely with a rolling pin or your hands. Melt butter, mix with crumbs and press into a springform pan lined with parchment paper. Cut the rhubarb into small pieces, boil it down together with the strawberry quarters, 100 g sugar, vanilla sugar, three tablespoons lemon juice and 100 ml water. At the end, add a tablespoon of cornstarch dissolved in a little water and boil up again, let cool. Set aside some compote for decoration.
Mix Philadelphia, yogurt and remaining lemon juice with electric hand mixer. Soak gelatin in 150 ml cold water for 10 minutes. Add remaining sugar and heat everything, stirring occasionally, until gelatin is dissolved. Stir briskly into the Philadelphia cream. Fold in strawberry-rhubarb compote. Pour cream into springform pan, chill Philadelphia Strawberry Rhubarb Cake for at least 3 hours. Decorate cake with remaining compote before serving.