Cut the sponge cake roulade into 8 slices, each 2 cm thick. Coat the inside of eight 6 cm diameter dessert rings with oil and sprinkle with granulated sugar. Insert the sponge cake slices.
For the cream, soak the gelatin in cold water according to package directions. Whip the cream with sugar until stiff and mix with the yogurt. Squeeze out the gelatine and gently warm it to 40 °C in a saucepan with the lemon juice. Stir in the raspberry puree and finally fold in the whipped cream. Spread the mixture on the prepared sponge cake bases.
For the jelly, mix agar agar and sugar, stir into the boiling water and boil for one minute. Add lemon juice and raspberry puree and let the mixture cool down to about 35 °C. Then spread it on the cream layer with a spoon.
Before serving, garnish the tartlets with fresh raspberries, whipped cream and chocolate leaves to taste.