Knead together flour, almonds, butter, sugar, vanilla sugar and egg yolk until it hold together and everything is evenly combined Wrap in plastic film and place in the fridge for 30 minutes.
Preheat oven to 200 C / Gas 6.
Line the bottom of a greased springform tin with the pastry. Prick several times with a fork and bake until golden brown, about 10 minutes. Take out of the oven and let cool.
Mix gelatine with 6 tablespoons cold water and set to one side for 10 minutes.
In a bowl stir together yogurt, sugar, salt, lemon zest and juice. In a separate bowl whip cream until stiff. Fold whipped cream into the yogurt mixture.
Heat gelatin in a small saucepan until completely dissolved. Place into a bowl and add a few tablespoon of the yogurt creme. Stir it in in quickly then gradually add the rest.
Put the baked pastry base on a cake plate. Place the springform rim around it and spread the yogurt creme on top. Refrigerate until the creme has set, which can take several hours.
In a small saucepan heat raspberries with sugar. In a bowl combine cornflour and a few tablespoons cold water and stir to dissolve. Pour into the pan with the raspberries and bring to the boil, stirring constantly. Continue cooking until mixture is glossy and thickened.
Remove from the heat and let cool, stirring constantly. Spread on top of the yogurt cake. Place the cake back into the fridge to chill.
Thinly peel the lemon in fine strips. In a small saucepan heat water and sugar and cook lemon strips over low heat, until thick and syrupy. Take lemon peel out of the syrup, drain and decorate the cake.