Place the venison in a large bowl and coat with 2 tablespoons oil, garlic, half the thyme, the juniper berries and peppercorns. Cover and refrigerate overnight.
When ready to cook, remove from the marinade and season with salt and pepper.
Sear in a very hot pan for 1 minute on each side, or until coloured all over. Remove from the pan, wrap in cling film and allow to rest in the fridge until ready to eat.
Preheat the oven to 180C/160C Fan/Gas 4.
Line a deep ovenproof dish with kitchen foil and place the beetroots inside. Bring the sides of the foil up around the beetroots, leaving a small gap. Pour the sherry vinegar and red wine vinegar into the foil, add ½ teaspoon salt, the sugar and remaining thyme, then seal the foil.
Pour 100–200ml/3½–7fl oz water around the foil into the tray (depending on saucepan size) and roast for 30–40 minutes, or until soft. Remove from the oven and allow to cool in the juices. Peel and roughly chop.
Place the celeriac in a saucepan with the milk and cream over a medium heat. Cook until soft, season with salt and pepper and blend using a hand blender. Set aside.
Meanwhile, in a bowl, mix the remaining 3 tablespoons oil with the white wine vinegar, mustard and a pinch of salt and pepper. Stir in the cherries.
Preheat a deep-fat fryer to 180C (CAUTION: hot oil can be dangerous. Do not leave unattended.). Deep-fry the kale in batches for 1 minute. Remove and drain on kitchen paper. Set aside.
Slice the venison into thin pieces and divide equally between four plates. Garnish with the beetroot, cherries, a few drops of celeriac purée and the kale.