Preheat oven to 180°C and line a 30x40cm baking tin with greaseproof paper.
Cream the butter and sugar for the apple cake until pale and fluffy.
Beat in the eggs one by one.
Sieve in the dry ingredients and fold together.
Stir in the soured cream and chopped apples.
Bake in the tin for 30 minutes until golden.
Line a 30cm Swiss roll tin and whisk egg whites with salt to soft peaks.
Whisk in sugar and lemon juice until stiff peaks form.
Spread onto the tray and sprinkle with hazelnuts, cinnamon, and sugar.
Bake at 180°C for 8–10 minutes and leave to cool on a kitchen cloth.
Whisk cream with sugar and fold in blackberries.
Spread the cream on the meringue and roll up.
Heat blackberries, sugar, and 570ml water for 6–8 minutes.
Blend the mixture until smooth.
Sieve the liquid and divide into two batches, adding soaked gelatine to one batch.
Pour the gelatine mixture into a container to set.
Cut the set jelly into small cubes.
Fry chopped apples with butter and sugar for 8–10 minutes.
Blend the fried apples into a smooth purée.
Soften apple wedges in butter and stir in sugar.
Cook until the apple wedges are caramelized.
Serve roulade slices with cake squares, purée, jelly, caramelized apples, and coulis.