Soften the butter to room temperature. Break up the biscuits in a food processor until you have a fine breadcrumb consistency. Mix into the butter. Line six stainless steel rings with acetate paper. Arrange the rings on a non stick baking sheet and cover the base of each ring with the biscuit mix. Chill in the fridge until the base is firm.
Peel the oranges and cut the zest into very thin strips. Dip the zests into boiling water for 30 seconds and refresh in cold water. Repeat this process.
Boil the water and caster sugar until you have a syrup. Add the zest and cook for 5 - 10 minutes until the liquid is reduced and all of the zests are coated with the syrup. Remove from the pan and dust with caster sugar. Set aside and allow to dry.
Break the chocolate into small pieces and place in a heatproof bowl.
Whisk the sugar and egg yolks together in a separate bowl.
In a saucepan, bring the milk and cream to the boil, pour onto the eggs and sugar and stir. Return this mixture to the saucepan and cook over a low heat until the mixture thickens and coats the back of a spoon. Remove from the heat and pour the mixture onto the chocolate though a fine sieve. Stir with a spoon until the chocolate is melted and the mixture is glossy. Allow the mixture to cool for 5 minutes and then pour into the rings. Refrigerate until the chocolate is set.
Whip the double cream and icing sugar until thick and then fold in the mascarpone cheese. Place in a piping bag and refrigerate.
Dust the top of the torte with cocoa powder. Place the torte in the midle of the plate. Remove the steel ring and the acetate lining. Pipe on the mascarpone and finish with a few pieces of candied orange zest.
«You can make this torte in a larger ring for 6 people. Vary the flavour by using a different citrus fruit for the candied zest.»