Rinse the soaked chickpeas, cover with water, and cook with the potato until tender. This could take 30 – 45 minutes but just check periodically by tasting one.
Remove the outer skin and green tops from the leeks, slice lengthways from the root up. Wash carefully and slice finely. Warm a large pot, and add the oil and margarine. Add the leeks and garlic to the pot and sweat gently with a good pinch of salt until tender and sweet (about 7 to 10 minutes).
Add the drained chick peas and potato and cook for 1 minute. Add about 4 cups of stock and simmer for 15 minutes.
To finish, you can leave it as a chunky broth, or purée with a hand blender for a smooth creamy soup, or divide the mixture in half. Using a hand blender or potato masher, puree half the mixture and fold back in the other half to give a creamy soup with a bit of bite to the texture.
Add the remaining stock until you get the consistency you prefer. Check for seasoning, add salt & pepper to taste and sprinkle a little cheese over each serving.