To make the Swiss rolls, preheat the oven to 180C/160C fan/gas 4. Grease the 2 Swiss roll baking tins and line them with baking paper. In a large bowl, beat the egg and sugar together with an electric whisk for about 5 minutes or until light and pale. Gently fold in the flour with a metal spoon. Divide between the two baking pans and bake for 10-12 minutes or until the sponges are lightly golden and cooked through.
Sprinkle some extra caster sugar on two sheets of baking paper and then turn the sponges over the sugared paper. Pull the paper off the bottom and, while still warm, roll up from the short end into a tight spiral using the paper to help. Let cool.
To make the lemon curd, place the egg yolks, granulated sugar, butter, lemon zest and lemon juice in a glass bowl over a pan of simmering water (don’t let the bowl touch the water). Whisk until combined, whisking continuously as the curds cook until thickened. This should take about 15 minutes. Pour into a clean bowl and set aside to cool.
To make the St. Clemens jelly, soak the gelatine leaves in cold water for 5 minutes to soften them. Peel 6 strips of a lemon and 6 strips of an orange with a vegetable peeler and place in a saucepan with the sugar and 400 ml of water. Bring to a boil over medium heat, stirring occasionally until sugar has dissolved. Remove from heat and discard the peel. Squeeze the water from the gelatin and stir in the pan until dissolved and let cool. Squeeze the lemons and oranges so you have 150ml/5fl oz of both lemon and orange juice. Stir the pan and strain the jelly through a fine sieve into a pitcher and allow to cool until cooled but not set.
To make the custard, place the cream in a saucepan over low heat and bring to a boil, stirring occasionally with a wooden spoon. In a bowl, whisk together the egg yolks, sugar, cornstarch and lemon extract, then gradually pour the hot cream into the bowl while whisking continuously. Immediately return to the pan and continue beating over low heat until the custard is thick and smooth. Pour the custard into a pitcher or bowl, line the surface with baking paper and let it cool.
To make the amaretti cookies, preheat the oven to 180C/160C Fan/Gas 4. In a large bowl, beat the egg whites until stiff. Gently mix in the sugar and almonds. Add the amaretto and gently fold in until you have a smooth paste.
Place some baking paper on a baking tray and brush lightly with butter or oil. Using a teaspoon, place small mounds of the mixture about 2cm apart as they will expand during cooking. Bake for about 15-20 minutes or until golden brown. Remove from oven and set aside to cool.
Strain two cans of mandarins to make the thick mandarin coulis. Discard the juice and put the fruit in a saucepan with the sugar and heat gently until broken. Remove from fire. In a small bowl, deglaze the arrowroot with 2 tablespoons cold water and add to the warm mandarins. Add the lemon juice and mix well before pouring into a large bowl. Strain the remaining two cans of mandarins and add the fruit to the bowl and let cool completely.
To suspend the jeweled chocolate, if the skin feels wet or sticky, roll in the caster sugar to absorb moisture. Melt the white chocolate in a bowl over a pan of gently simmering water. Pour the white chocolate onto a baking tray lined with baking paper and sprinkle the mixed zest over it. Let it set and then break into shards.
Before assembling, roll out the cooled Swiss rolls and spread them with the lemon curd. Roll up again and cut one into 1 inch (1 inch) slices and place upright around the bottom of the trifle dish so that the swirl is visible. Cut the other Swiss roll into thicker pieces and use to fill the bottom of the dish, making sure the top is about the same height as the slices along the edge. Use leftover sponge to fill in any gaps.
Pour the St Clement’s jelly over the Swiss roll layer and set aside in the fridge to set completely. This takes about 3 hours. When ready, pour over the custard and arrange a single layer of amaretti biscuits, keeping a few for the top. Pour over the mandarin coulis. In a large bowl, whip the cream until soft peaks form and spoon over the coulis. Crumble the remaining amaretti cookies over it and decorate with the pieces of chocolate bark.