Cook the lemon juice, 400 g of sugar, 1 x vanilla bean, and 1 liter of water together until it forms a syrup. Peel, halve and de-core the peaches, place in a vacuum bag with the syrup, vacuum seal and cook sous-vide in a water bath at 75 °C (165 °F). Leave to cool.
Pistachio Ice Cream
Finely chop the pistachio nuts in a blender. Bring the milk, heavy cream, 1 x vanilla bean, finely-chopped pistachios and 125 g of sugar to a boil. Leave to cool for a little while. Whisk sugar together with 10 x egg yolks until fluffy, then work in to the milk and cream mixture, stirring constantly. Simmer over a low heat until thickened. Flavor with the bitter almond oil and Kirsch liqueur, remove from the heat and place in a Pacojet, then freeze. Pacojet the pistachio ice cream before serving.
Whisk together 7 x egg yolks and 115 g of sugar until fluffy (the sugar must be completely dissolved). Gradually work in the champagne and froth up over a water bath. Pass through the iSi funnel & sieve directly into a 0.5 L iSi Whipper. Screw on 1 iSi cream charger and shake vigorously. Keep the iSi Whipper warm at 75 °C (165 °F) in a bain-marie or water bath.