For the rye and poppy seed biscuits, mix together all the ingredients for the biscuits with two tablespoons of water. Wrap into a ball and cover in cling film. Leave to chill in the fridge.
For the beetroot jelly, line a 20cm/8in circular loose-bottomed cake tin with baking parchment. Blend the beetroot using a hand-held blender or food processor and strain the beetroot to retain the liquid (you will have about 100ml/3½fl oz liquid). Pour into a small pan and add the other ingredients for the jelly. Bring to the boil.
Pour the jelly mixture into the lined tin and leave in the fridge to chill.
For the rye and poppy seed biscuits, grease a baking tray. Roll out the biscuit dough and, using a 3cm/1¼in diameter biscuit cutter, cut out circles. Transfer to the prepared baking tray and place in the freezer.
Preheat the oven to 180C/fan oven 160C/350F/Gas 4.
Mix the crème fraîche in a bowl with some salt and pepper and the chopped tarragon. Spoon into a piping bag fitted with a small plain nozzle. Set aside.
Bake the biscuits for 20-25 minutes, or until golden-brown – check after 15 minutes to make sure they aren’t cooking too fast. Remove from the oven and leave to cool on a wire rack.
Once cool, pipe the crème fraîche onto the biscuit bases. Cut circles of beetroot jelly using the biscuit cutter you used for the biscuits and put on top of each. Serve.