Heat the olive oil in a large casserole dish over a medium heat. Sweat the leek, celery and carrot for 5-6 minutes, stirring frequently. Add the beetroot, potato and carrot and continue to cook for 5 minutes, stirring occasionally. Add the stock, bring to the boil, then reduce to a simmer.
Simmer for 45 minutes until all the vegetables are very soft. Remove the soup from the heat and puree briefly with a stick blender to thicken it. Season to taste and spoon into serving bowls. Garnish with some sour cream, chopped dill and more salt and black pepper.
Freezing and defrosting guidelines
Make the soup, then leave to cool at room temperature. Freeze (without garnishes or toppings) in a rigid container, leaving a bit of space for expansion, for up to 1-3 months. Reheat either from frozen or defrost in the fridge overnight. Once piping hot, add toppings or garnishes and serve.