For the shallot ash, preheat the oven to 200C/180C Fan/Gas 6. Heat the oil in a heavy-based, ovenproof frying pan over a high heat. Place the shallots face down in the pan and place a heavy weight, such as another pan, on top of them.
When you can hear the shallots start to sizzle, transfer the pan to the oven for 20 minutes, or until the cut sides of the shallots are caramelized and almost blackened. The weight should remain on the shallots the whole time. Leave to cool and then peel off and discard the skins.
Blitz the flesh and any liquid from the pan in a blender until it looks like a rough jam. Season with salt and spread out on a baking sheet covered in baking paper. Place in a dehydrator at 60ºC overnight or in an oven at its lowest temperature for 3 hours.
Blitz the dehydrated mixture in a blender or food processor until it resembles a sticky compost. Return this mixture again to the dehydrator or oven for another 4 hours. Blitz for a final time until it looks like fine, damp soil. Set aside.
For the tartare, cut the venison into slices that are about 5mm/¼in thick. Lay the slices flat on a freezerproof plate covered in baking paper and place in the freezer for a few hours, or until frozen. Cut the frozen slices into diced pieces. Spread the frozen dice out on a shallow dish and bind tightly in cling film.
Poke a small hole in the cling film and smoke with the oak shavings, using a smoking gun or similar cold smoker. Cover the hole to prevent the smoke from escaping. When the venison has come to room temperature and is very smoky, place in a large bowl and mix together with all the other tartare ingredients. Set aside.
For the beer and shallot purée, preheat the oven to 200C/180C Fan/Gas 6. Place the shallots in a heavy-based, ovenproof frying pan and drizzle with the oil. Season with salt and roast in the oven for 20 minutes, or until the outsides are blackened but the insides remain soft and sticky.
Transfer the shallots to a bowl and deglaze the pan with the beer, reducing the beer down to a syrup. Stir in the butter and sugar. Place the beer mixture and the shallots in a blender or food processor and blitz thoroughly until smooth, adding the xanthan gum while the blender is running. Season with salt and strain the mixture through a fine sieve. Leave to cool.
For the cep croûtons, preheat the oven to 190C/170C Fan/Gas 5. Tear the bread into 1cm/½in chunks. Melt the butter in a frying pan and stir in the cep salt and then the bread chunks. Tip the croûtons out onto a baking tray and roast for 8 minutes. Pour the butter from the tray carefully away, give the croûtons a quick toss and return to the oven for 5 minutes, or until they turn a deep golden brown.
Divide the tartare between four serving plates and sprinkle with the remaining shallot ash and cep croûtons. Spoon over the beer and shallot purée and serve with the garlic shoots, leaves and flowers scattered on top.