Preheat the oven to 120'C.
Cut the bottom from the pears and then slinly slice them using the finest setting on a mandolin. Mix together the elderflower, lemon juice and sugar to be used in the bavarois. Dip the slices into the elderflower, lemon and sugar mixture and then lay flat between two sheets if baking parchment between two trays. Reserve the liquid to be used in the bavarois. Transfer to the oven and cook for 3 to 4 hours until light and crispy.
Make a custard: place the gelatine leaves in a bowl of cold water to soften. Split the vanilla pod in half and scrape out the seeds. Add the vanilla seeds and the sugar to the eggs yolks and whisk together. Place the empty vanilla pod in a saucepan with the milk and 200ml cream. Bring the milk and cream to the boil and then add this liquid to the egg yolk mixture. Whisk together and then return to a gentle heat and cook until the mixture thickens and coats the back of a spoon. Add the softened leaves to the pan, stir to dissolve and then leave to cool.
Make a pear puree: peel the four pears, remove the cores and cut the fruit into large cubes. Place in a saucepan with the elderflower cordial, lemon juice and sugar mixture used to flavour the pear crisps. Cook until soft and then blend to a smooth puree. Leave to cool.
Whisk the remaining cream to soft peaks. Fold the pear puree into the custard until fully incorporated. Gently fold in the whipped cream. Pour the bavarois mixture into stainless steel rings and chill in the fridge until set.
Soften the gelatine leaves in cold water. Place the elderflower cordial and the white wine in a saucepan and warm to body temperature. Squeeze the gelatine leaves dry and then dissolve into the warm liquid. Pour the mixture into a siphon and charge with gas. Refrigerate until ready to serve.
Warm the sides of the moulds and then carefully remove them to get the bavarois out. Place the bavarois in the centre of the plate, garnish with the pear crisps and the elderflower foam.
«Make sure you don't overcook the eggs when making the custard - don't bring the mixture back to the boil once combined with the milk and cream. Simply cook over a gentle heat until it begins to thicken.»