Heat the oil in a large saucepan over a medium-low heat. Add the chopped spring onions and garlic, and cook for a couple of minutes, until fragrant. Add the diced potatoes and cook for a further 2 minutes.

Next add the vegetable stock cube and water (or use liquid stock, if you prefer), along with the dried herbs, and plenty of salt and pepper. Bring to a simmer, and cook for around 20 minutes, until the potatoes are completely soft. You should be able to easily squash them with the back of a spoon.

Remove the pan from the heat, and add the sour cream. Use a hand blender to blend the soup until it is completely smooth.

Add more salt and pepper to taste, if needed, and serve topped with more sour cream and spring onions, if desired.