Heat the oil in a pan. Add the onions, garlic and ginger and sauté for approx. 2 mins. Add the beetroot, cook briefly, pour in the water, bring to the boil, season. Reduce the heat, cover and simmer for approx. 20 mins. over a low heat. Pour in the lemon juice, simmer for approx. 2 mins., blend the soup until smooth.
Toast the nuts and linseed in a pan over a medium heat. Add the sugar, continue toasting, shaking the pan occasionally until all the sugar and lemon juice has dissolved. Remove the pan from the heat, immediately tip the nuts out onto a sheet of baking paper, allow to cool. Coarsely chop the nuts.
Serve the soup in bowls, garnish with crème fraîche, nuts, crisps and chervil.