To make the Swiss rolls, preheat the oven to 180C/160C Fan/Gas 4. Grease and line the 2 Swiss roll tins with baking paper. In a large bowl, beat the egg and sugar together with an electric hand whisk for approximately 5 minutes or until light and pale. Using a metal spoon, gently fold in the flour. Divide between the two tins 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 then turn the sponges out onto the sugared paper. Peel off the paper from the underside and, while still warm, roll them both up from the short end into a tight spiral using the paper to help. Leave to cool.
To make the lemon curd, place the egg yolks, granulated sugar, butter, lemon zest and lemon juice in a glass bowl over a saucepan of simmering water (don’t let the bowl touch the water). Whisk until combined and whisk continuously as the curd cooks until thickened. This should take about 15 minutes. Pour into a clean bowl and set aside to cool.
To make the St Clement’s jelly, soak the gelatine leaves in cold water for 5 minutes to soften. Using a vegetable peeler, peel 6 strips from a lemon and 6 strips from an orange and put these into a saucepan with the sugar and 400ml/14fl oz water. Bring to a simmer over a medium heat, stirring occasionally until the sugar has dissolved. Remove from the heat and discard the peel. Squeeze the water out of the gelatine and stir into the pan until dissolved then leave to cool. Squeeze the lemons and oranges, so you have 150ml/5fl oz of both lemon and orange juice. Stir into the pan then strain the jelly through a fine sieve into a jug and chill until cool but not set.
To make the custard, place the cream in a saucepan over a gentle heat and bring it up to simmer, stirring occasionally with a wooden spoon. In a bowl, whisk together the egg yolks, sugar, cornflour and lemon extract, then gradually pour the hot cream into the bowl whilst whisking continuously. Immediately return the whole lot back to the saucepan and continue whisking over a gentle heat until the custard is thick and smooth. Pour the custard into a jug or bowl, cover the surface with greaseproof paper and leave to cool.
To make the amaretti biscuits, preheat the oven to 180C/160C Fan/Gas 4. In a large bowl, beat the egg whites until firm. Mix the sugar and almonds gently into it. Add the amaretto and fold in gently until you have a smooth paste.
Place some baking paper on a baking tray and lightly brush with butter or oil. Using a teaspoon, place small heaps of the mixture approximately 2cm/¾in apart, as they will expand during cooking. Bake for approximately 15–20 minutes or until golden brown. Remove from the oven and set aside to cool.
To make the chunky mandarin coulis, strain two tins of mandarins. Discard the juice and put the fruit into a saucepan with the sugar and heat gently until broken down. Remove from the heat. In a small bowl, slake the arrowroot with 2 tablespoons cold water then add to the warm mandarins. Add the lemon juice and mix well before pouring into a large bowl. Strain the remaining two tins of mandarins and add the fruit to the bowl then leave to cool completely.
To make the jewelled chocolate bark, if the peel feels wet or sticky, roll in the caster sugar to absorb any moisture. Melt the white chocolate in a bowl sitting over a saucepan of gently simmering water. Pour the white chocolate onto a baking tray lined with baking paper and scatter over the mixed peel. Leave to set then break into shards.
To assemble, unroll the cooled Swiss rolls and spread with the lemon curd. Roll back up again and slice one into 2.5cm/1in slices and place upright around the bottom edge of the trifle dish so the swirl is visible. Slice the other Swiss roll into thicker pieces and use these to fill the bottom of the dish, ensuring the top is roughly the same level as the slices that line the edge. Use off-cuts of sponge to fill any gaps.
Pour the St Clement’s jelly over the Swiss roll layer and set aside in the fridge to completely set. This will take approximately 3 hours. Once set, pour over the custard then arrange a single layer of amaretti biscuits, keeping a few back for the top. Pour over the mandarin coulis. In a large bowl, whip the double cream until soft peaks form then spoon this over the coulis. Crumble over the reserved amaretti biscuits and decorate with the chocolate bark shards.