Begin by fermenting the rye, as this needs to be done 6-7 days in advance. Combine all the ingredients in a sterilised 2-litre Kilner jar, then seal the lid and store in a dark place at room temperature for 6-7 days. Open the lid every few days to allow built-up gas to escape

Make the dill oil by placing the picked dill leaves and oil in a blender and blitz on high speed for 5 minutes, until smoking hot and completely smooth. Hang the mixture in a muslin cloth or j-cloth in a sieve set over a bowl in the fridge to filter the oil. Reserve until ready to serve

For the base place the sausages in a saucepan. Give the tongue a good rinse and then place it in the pan with the sausages and cover with cold water. Add the salt, bring to the boil and skim off any scum that rises to the surface

Once the water is boiling and you have removed the scum, roughly chop the vegetables and add them to the pan along with the rest of the ingredients. Bring to a simmer and leave to cook for 3½ hours

After this time, check the tongue is cooked – it should be soft when pierced with a knife. Leave to cool in the stock, then pass the stock through a fine sieve and reserve the tongue in the fridge. If you are not using the tongue, then the sausage can be reserved and served instead

If using a barbecue to cook the potatoes (the best method), light a barbecue and wait for the flames to die down, leaving you with glowing coals. If using an oven, preheat it to 200°C/gas mark 6

While the barbecue or oven heats up, finish the soup. Place 500g of the fermented rye mixture (discarding any bay leaves or allspice berries), 1 litre of the strained stock, the sour cream, horseradish and garlic clove in a large saucepan and bring to the boil. Once boiling, transfer the soup to a blender and blitz until smooth, then pass through a fine sieve into a pan ready to reheat for serving

Once the coals in the barbecue are glowing, bury the potatoes amongst the embers and leave to cook for 15-20 minutes, until charred on the outside and soft in the middle. If using the oven, cook for 30-45 minutes until tender

If using the tongue, peel away the hard skin and then dice the tongue into 1cm cubes (otherwise, dice the sausages). Once the potatoes are cooked, dice those into 1cm cubes too. Heat a dash of oil in a frying pan and cook the tongue and potatoes to crisp them up, checking for seasoning as you do so. Meanwhile, gently reheat the soup

To serve, divide the tongue (or sausage) and potatoes between 4 bowls, arranging them into a pile in the centre. Top with chopped dill and a grating of fresh horseradish

Combine the dill oil and the hot soup – the best way to do this is pour the oil into a jug, then top with the hot soup. This means that once it’s poured into the bowls, the oil will split the soup and create a speckled appearance. Pour the soup into the bowls around the potatoes and tongue and serve