Preheat oven to 160°C, 300°F, Gas 2.
Wrap half the beetroot and the golden beetroot in foil, place on a tray lined with rock salt and cook in the preheated oven for 11/2 hours, then leave to sweat in foil for 10 minutes.
Peel the golden beetroot and use a 1.5cm diameter pastry cutter to make four fondants. Peel the other cooked beetroot, cut out four more fondants and chop the remaining beetroot.
Scrape the seeds from the vanilla pod and mix with the olive oil. Store the beetroot fondants in this oil.
To make the soup, peel the remaining raw beetroot and chop. Place in a blender with the chopped cooked beetroot, apple juice and beetroot juice. Blend until smooth, then pass through a fine sieve by tapping lightly – don’t try to push the pulp through, as you just want the juice. Put the liquid in a bowl over a bowl of iced water.
Season the soup with salt. Then add the sherry vinegar to accentuate the salt, then add some sugar, which should balance both flavours. Pass again though a sieve and refrigerate.
Peel the avocados and use the pastry cutter to make four fondants. Coat in lemon juice and set aside.
To make the avocado sorbet, add the sugar to 100ml/4fl oz water and bring to the boil until it becomes syrup. Blend the rest of the avocado in a blender and add the cooled syrup. Pass through a fine sieve and add the lime and lemon juice, plus rinds. Transfer to an ice cream machine and churn until frozen.
Heat 2 tbsp water, add the gelatine and a little vodka and leave the gelatine to dissolve slowly. Remove pan from the heat and add the remaining vodka. Pass the jelly through a fine sieve into a small container and set in the fridge for a few hours – don’t worry if it goes cloudy.
To serve, recheck the seasoning of the soup and pour into four chilled bowls. Add the beetroot and avocado fondants, spoon in some of the vodka jelly and avocado sorbet and garnish with a few coriander leaves.