Grease a 20cm/8in loose-bottomed tart tin.
On a lightly floured work-surface, roll out the sweet pastry to a size large enough to line the tart tin with a little excess all around.
Line the tart tin with the pastry, pressing the pastry into the edges. Trim off the excess pastry with a sharp knife and cover with cling film. Place into the fridge to chill for 30 minutes.
Preheat the oven to 180C/360F/Gas 4.
Remove the tart case from the fridge and uncover. Line the pastry with baking parchment then fill with baking beans (or uncooked rice).
Transfer to the oven to bake blind for 10-15 minutes, then remove the greaseproof paper and baking beans (or rice) and return to the oven to bake for a further 3-5 minutes, until it is just cooked and golden-brown. Remove from the oven and set aside.
Reduce the oven temperature to 170C/345F/Gas 3.
Meanwhile, place the chocolate into a heatproof bowl and place over a pan of barely simmering water (do not let the water touch the base of the bowl). Leave to heat until melted, then remove the bowl from the heat.
Add the cream and the egg yolks and whisk into the chocolate until combined.
Carefully pour the chocolate mixture into the pre-cooked pastry case, smoothing out the mixture to fill the case to the edges.
Place the chocolate tart into the oven to bake for 15 minutes, or until the chocolate filling is just set. Remove from the oven and allow to cool to room temperature before serving.
For the Turkish delight, line a 23cm/9in square deep baking tray with baking parchment.
Place 350ml/12½fl oz of the water, the cornflour and cream of tartar into a separate pan and whisk together well. Place over a medium heat and cook until the mixture has thickened.
Meanwhile, place the sugar and the remaining 200ml/7fl oz water and the lemon juice into a pan and place over a medium heat. Bring to the boil and heat to 116C/240F (you will need a sugar thermometer).
When the sugar and water mixture has reached 116C/240F, add the cornflour mixture and whisk vigorously to combine. Return to the heat and cook over a low heat for 20-30 minutes, until thickened and light golden-brown.
Remove from the heat, add the rosewater and stir well.
Pour the Turkish delight mixture into the parchment-lined tray and smooth to the edges. Allow to cool, then transfer to the fridge to chill for 1-2 hours, or until completely set.
When the Turkish delight is set, dust a piece of baking parchment with icing sugar, then turn out the set Turkish delight onto the paper. Cut the Turkish delight into squares.
Dust one third of the squares with icing sugar and set aside.
Dip the remaining squares of Turkish delight into the melted chocolate and place onto a plate. Place into the fridge to chill and for the chocolate coating to set.
To serve, place a slice of the chocolate tart into the centre of each plate. Place two pieces of chocolate-coated Turkish delight and one piece of plain Turkish delight alongside. Serve with a spoonful of vanilla ice cream.