Peel and chop the beetroots including the stalks. Put them in a pan, add a pinch of sugar and cover with cold water (just a little bit more to cover the beetroots). Put the lid on and bring to the boil, reduce the heat immediately and simmer for around 40 minutes until soft. A couple of minutes towards the end of the cooking process I like to add 1-2 tablespoons of red wine vinegar or a good squeeze of lemon. Take the pan off the heat and leave to cool for around 2 hours.
Put the feta cheese, natural yogurt, cooked beetroots and cooking liquid into a blender and blend until a smooth consistency.
Leave in a fridge to cool for a minimum of 2 hours.
Before serving give it a good stir. Check for seasoning but I would be careful here, the Feta cheese for me it is salty enough. You may want to add some black pepper after serving on a soup plate.
Divide the soup between serving dishes, garnish with a dollop of greek yogurt or crème fraîche in the middle of the soup, add chopped apple and sprinkle with fresh dill.