Carrot soup with sweet potatoes

This is a lovely soup. I love the sweetness of the carrots and the sweet potatoes!
I don't really have any specific measures, but it's really just a question of taste and amount of people.

Another variant I do is replace the sweet potatoes with regular potatoes (so much cheaper), and add some finely grated ginger.

8 Carrots
2 (SMALL!) Sweet potatoes
1 Onion
1 Clove of garlic
2 Vegetable stock cubes
2 Tablespoons of thick youghurt, milk, or cream
Enough water to almost cover the carrots.
1 Orange

Chop the onion and the garlic, sizzle it in oil in a pan.
Cut the carrots and potatoes into cubes.
Put them in the pan, add the stock and boil.
When the vegetables are done, take the pan of the heat.
Add the yoghurt and put the vegetables all in a blender.
Run until smooth.
Add juice from the orange.
Thin down the soup with the stock.
Re-heat and serve with a nice bread.