For the salted caramel, place the dark muscovado sugar and cream in a saucepan. Using thoroughly wet hands and spoon, add the glucose to the sugar and cream mixture and bring the mixture to the boil. (NB: Glucose sticks to dry hands and spoons.)
Meanwhile, heat the caster sugar in another pan over a low heat, stirring continuously until golden-brown and caramelised. Remove from the heat instantly.
Carefully, pour the hot cream and glucose mixture over the caramelised sugar (the mixture may splutter) and return the mixture to a simmer. Continue to simmer until the caramel mixture has thickened and darkened and the temperature reaches 102C. (NB: Use a sugar thermometer to check the temperature of the caramel.)
Remove the pan from the heat and carefully stir in the lemon juice and salt. Season with freshly ground black pepper and stir gently once more. Set aside to cool slightly.
Pour the caramel into small silicone moulds or ice cube trays. When the caramel has completely cooled, freeze it for at least 2 hours, or until set. (NB: You will not need all of the caramel for this recipe. The remaining caramel can be stored in the freezer for up to 3 months.)
For the chocolate fondant, grease the insides of 4 ring moulds, 5cm/2in diameter and 6cm/2½in deep, with softened butter.
In a bowl, mix together the cocoa powder and caster sugar until well combined. Dust the inside of the ring moulds with the mixture, shaking off any excess. Place the prepared ring moulds onto a baking tray lined with greaseproof paper.
Melt the chocolate and butter in a heatproof bowl set over a pan of simmering water (do not allow the base of the bowl to touch the water).
Meanwhile, place the eggs and egg yolk into a bowl and whisk together until pale and fluffy.
Sift the icing sugar into the whisked eggs, whisking until well combined. Next, sift in the arrowroot and whisk until the mixture is pale, thick, has doubled in volume and the beaters leave a trail on the surface of the mixture when lifted. (NB: This is called the ribbon stage.)
Whisk the melted chocolate mixture into the egg mixture until well combined.
Using a ladle, fill each of the prepared ring moulds with the chocolate fondant mixture until they are three-quarters full.
Add one piece of frozen caramel to the centre of each ring mould and press down so that it is nestled halfway down the mould. Gently push the chocolate fondant mixture over the caramel to cover it completely. Chill the chocolate fondants in the fridge for at least 30 minutes and up to 24 hours.
When the chocolate fondants have chilled, preheat the oven to 200C/390F/Gas 6.
Transfer the chilled chocolate fondants to the oven and bake for 5 minutes, or until the tops have just formed a crust. Remove the fondants from the oven and allow to cool.
When the fondants have cooled, run a butter knife around the insides of each mould to loosen the fondants. Carefully remove the moulds. Chill the fondants in the fridge for at least 30 minutes.
Meanwhile, for the chocolate sauce, heat the milk in a pan until just simmering. Add the chocolate and whisk well until smooth and well combined, then remove from the heat.
When ready to serve, preheat the oven to 180C/355F/Gas 4.
Bake the fondants for 8 minutes, or until the cakes have risen.
To serve, place a spoonful of the chocolate sauce into the centre of each of four serving plates, smoothing it out into an oblong. Dust the chocolate fondants with icing sugar and place on top of the puddle of sauce, in the middle. Sprinkle the caramelised pistachios and almonds around the plate. Place one quenelle of pistachio ice cream next to the fondant. Serve immediately.