To make the Swiss rolls, preheat the oven to 180C/160C Hot air/Gas 4. Grease and line the 2 Swiss roll molds with parchment paper. In a large bowl, beat the egg and sugar with an electric hand mixer for about 5 minutes or until light and pale. Using a metal spoon, gently stir in the flour. Divide between the two pans and bake for 10 to 12 minutes or until the sponges are lightly browned and cooked through.
Sprinkle a little extra caster sugar on two sheets of baking paper then turn the cookies over on the sugar paper. Peel off the bottom paper and, while still warm, roll them both up from the short end into a tight spiral, using the paper to help you. Let cool.
To make the lemon curd, place the egg yolks, caster sugar, butter, lemon zest and lemon juice in a glass bowl over a saucepan of simmering water (do not let the bowl touch the water). Whisk until combined and whisk continuously as the curd cooks until thickened. This should take around 15 minutes. Pour into a clean bowl and let cool.
To make the St Clément jelly, soak the gelatin sheets in cold water for 5 minutes to soften them. Using a vegetable peeler, peel 6 strips of a lemon and 6 strips of an orange and put them in a saucepan with the sugar and 400 ml of water. Bring to a boil over medium heat, stirring occasionally, until the sugar has dissolved. Remove from the heat and discard the skin. Squeeze the water out of the gelatin and stir in the pan until it is dissolved then let cool. Squeeze the lemons and oranges to obtain 150 ml of lemon and orange juice. Stir into saucepan then strain jelly through a fine sieve into a pitcher and refrigerate until cold but not set.
To make the pastry cream, place the cream in a saucepan over low heat and bring it to a simmer, 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 continuing to whisk. Immediately return everything to the saucepan and continue whisking over low heat until the cream is thick and smooth. Pour the custard into a pitcher or bowl, cover the surface with parchment paper and let cool.
To make the amaretti biscuits, preheat the oven to 180C/160C Hot 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 smooth.
Place parchment paper on a baking sheet and brush lightly with butter or oil. Using a teaspoon, place small heaps of the mixture about 2cm apart, as they will puff up during cooking. Bake for about 15 to 20 minutes or until golden brown. Take out of the oven and let cool.
To make the large mandarin coulis, strain two cans of mandarin oranges. Discard the juice and put the fruit in a saucepan with the sugar and heat gently until broken down. Remove from fire. In a small bowl, soak the arrowroot with 2 tablespoons of cold water then add it to the warm mandarins. Add the lemon juice and mix well before pouring into a large bowl. Strain the remaining two cans of tangerines and add the fruit to the bowl, then let cool completely.
To make the jeweled chocolate bark, if the skin is damp or sticky, roll it in powdered sugar to absorb the moisture. Melt the white chocolate in a bowl over a saucepan of simmering water. Pour the white chocolate onto a parchment lined baking sheet and spread over the mixed zest. Leave to set then break into pieces.
To assemble, unroll chilled Swiss rolls and spread with lemon cream. Roll up again and cut one into 1”/2.5cm slices and place them upright around the bottom edge of the trifle dish so the swirl is visible. Cut the other Swiss roll into thicker pieces and use them to fill the bottom of the dish, making sure the top is about even with the slices that line the edge. Use scraps of sponge to fill in the gaps.
Pour the St Clement jelly over the layer of Swiss roll and set aside in the refrigerator so that it sets completely. It will take about 3 hours. Once set, pour over the custard then lay out a single layer of amaretti biscuits, keeping a few for the top. Pour over the mandarin coulis. In a large bowl, whip the double cream until it forms soft peaks then pour it over the coulis. Crumble the reserved amaretti cookies and decorate with the chocolate bark chips.