Blitz the beetroot in a food processor or chop finely by hand. Add the nuts, season. Stir in the eggs and mix to create a compact mass. On a baking tray lined with baking paper, use your hands to press the mixture into a rectangle approx. 5 mm thick.
Approx. 30 mins. in the centre of an oven preheated to 200°C. Remove from the oven, transfer to a cooling rack with the baking paper and leave to cool. Cut the beetroot flatbread into approx. 30 pieces.
Combine the crème fraîche with the chervil and lemon zest, season.
Place approx. 1 tsp of sauce on each of the slices of beetroot flatbread, top with the roast beef and caper berries, garnish with the chervil leaves.