In a frying pan over a medium heat, add your butter. Fry until bubbling. Chop all the vegetables into cubes and add to the butter your beetroot, carrot, red onion, winter cabbage and leek. Fry for 20-25 minutes.
Pour the cooked vegetables into a pan. Add your beef stock, vinegar, thyme, salt and pepper. Bring to the boil then turn down to a simmer.
Simmer for 10 minutes. Allow the mix to cool slightly before blitzing. Serve with a wedge of crusty, buttery sourdough!