Preheat the oven to 180°C (160°C fan, gas 4). Brush the base of the loaf tin with oil and dust with flour.
For the sponge, separate the eggs.
Beat the egg whites until stiff, add the sugar gradually and continue whisking until stiff and glossy.
Sieve the flour, cocoa and baking powder into a bowl. Beat in the egg yolks then fold in the beaten egg whites. Spoon into the tin, spread level and bake for 40 minutes until a skewer inserted into the centre of the cake comes out clean.
Remove from the oven, allow to cool for 10 minutes, then turn out and allow to cool completely on a wire rack. Level the top, then slice the cake horizontally into 3 layers.
For the cream, soak the gelatine in cold water. Crush the amaretti. Mix the yogurt with the sugar. Place the pressed gelatine and liquid in a saucepan, heat until the gelatine melts. Remove from the heat. Add the gelatine to the yogurt. Whip the cream until stiff. Stir 2-3 tbsp of the cream into the gelatine mix then fold in the remaining cream. Sprinkle over the amaretti.
Fold in with a spatula.
Line the loaf tin with cling film and place one of the sponge layers in the base.
Spread with a third of the cream.
Top with the second sponge layer.
Top with more cream and cover with the last sponge layer. Press lightly.
Finish with remaining cream and chill in the fridge for at least 3 hours.
To serve, turn out of the tin and peel off the cling film. Whip the cream unti stiff. Spread all over the cake and pipe rosettes with a piping bag. Grate the chocolate very finely on top and garnish the cream cake with jelly. Serve in slices.