For the cherry ripple ice cream, heat the cream, milk and vanilla pod until boiling. Remove from the heat and set aside to infuse for 5 minutes. Discard the vanilla pod.
Whisk the egg yolks and 110g/4oz of the sugar in a bowl until well combined. Pour the cream mixture onto the eggs, whisking continuously, until well combined.
Return the mixture to the saucepan and continue to heat over a low heat, stirring continuously until the mixture has thickened enough to coat the back of a spoon. (Do not allow the mixture to boil.) Set aside to cool completely.
Meanwhile, heat the the cherries, remaining caster sugar and water in a saucepan, until boiling. Boil for 4-5 minutes, or until the cherries have broken down, then blend in a food processor to a thick pureé.
Churn the mixture in an ice-cream machine to a soft consistency, then stir in the cherry pureé. Transfer to an airtight container and put into the freezer for at least two hours.
For the vermouth sabayon, bring a little water to the boil in a pan, then reduce the heat until the water is simmering. Suspend a heatproof bowl over the water (do not allow the base of the bowl to touch the water). Whisk the egg yolks and half of the sugar in the bowl until well combined.
Gradually whisk in 75ml/3fl oz of the vermouth until the mixture has thickened.
Place the pear wedges, remaining vermouth, remaining sugar and lemon juice into a pan and add enough water to just cover the pears. Simmer the mixture for 5-8 minutes, or until the pears are tender. Drain and pat dry with kitchen paper.
To serve, divide the poached pears, cherries and blackberries among four serving plates. Spoon the vermouth sabayon over the fruit and heat, using a cooks' blow torch until golden-brown. Scoop the cherry ripple ice cream alongside and serve immediately.