Preheat the oven to 180°C, 350°F, Gas 4. Roll out the pastry and line a 23cm/9in loose-bottomed flan tin. Chill for 30 minutes.
Place the flan tin on a baking sheet and cook for 25 minutes until golden brown. If the pastry bubbles during cooking, press down gently with the back of a spoon. Remove from the oven and leave to cool. Once cool, brush the base and sides with the warmed marmalade.
Prepare the filling by whisking the skimmed milk powder into the cold milk in a pan and heating to just below boiling point. Whisk in the cocoa, Cointreau, citrus zest, vanilla and chocolate essence. Leave to cool. Meanwhile, dissolve the gelatine in 3 tbsp of the hot water, then stir into the chocolate mix.
Bring the remaining 6 tbsp water to the boil. Whisk the egg yolks in a small metal bowl and keep whisking as you gradually add the boiling water. Set the bowl over a pan of hot water, stirring constantly, for around 4-5 minutes until the mixture reaches 160°F. Strain through a fine sieve into the chocolate mixture and stir in the Canderel. Stir until smooth.
Pour the filling into the pastry, smooth the top then cover with clingfilm and chill overnight. Serve cut into wedges with crème fraîche and fresh orange segments, if liked.