Line a round cake or tart tin with baking parchment.
Place the butter in a saucepan and melt over a low heat. Place the biscuits in a food processor and blitz to a coarse crumb. Add the butter to the biscuits and combine well.
Add the mixture to the cake tin and press them firmly down to create the base of the torte. Chill in the fridge while you prepare the rest of the recipe.
Peel the oranges and cut the zest into very thin strips. Blanch the zests in boiling water for 30 seconds and refresh in cold water. Repeat this process a second time.
Mix together the water and caster sugar and then bring to the boil. Reduce to a thick a syrup. Add the zests to the syrup and cook for 5 - 10 minutes. The syrup will have reduced even further and be coating all of the zests. Remove from the pan and dust with caster sugar. Leave to dry on baking parchment.
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 the liquid on to the eggs and mix together. Return to the pan and cook over a low heat until the mixture thickens and coats the back of a spoon. Remove from the heat and pour this mixture over the chocolate. Stir continually until all of the chocolate has melted and you have a smooth and glossy mixture. Leave to cool for 5 minutes and then pour the mixture over the biscuit base, smoothing out the top with a palette knife if necessary. Chill in the fridge for at least 4 hours or until set.
Dust the top of the torte with cocoa powder before cutting into slices. Finish with a few pieces of candied orange zest.
«Make sure the biscuit base is well chilled before pouring the chocolate mixture on top. This will prevent the base becoming soggy.»