This weekend I devised a soup which has no potato, but still has a smooth texture and is plenty filling. Here 'tis:
olive oil
1 small onion
1 medium leek
2 sticks of celery
a large carrot
1 clove garlic
1tsp tumeric
4 good handfuls of red lentils
about 2 litres of stock. I used chicken stock from the freezer and supplemented that with a tbsp of vegetable stock powder.
salt and pepper
Slosh some oil into a large pan (I used my pressure cooker) and heat. Chop the veg and garlic into whichever size you fancy (I was having a small day yesterday), and sautee gently in the oil for about five minutes. Add a tsp of tumeric and stir. Chuck in the lentils and stir them around to coat with the oil, then add the stock, a good pinch of salt and some pepper.
At this point I brought the soup to a simmer and pressure cooked it on high for ten minutes. This meant that the lentils almost completely disintegrated, leaving a smooth sauce for the rest of the vegetables to sit in. If you don't have a pressure cooker* then could probably need to simmer the soup for at least 50 minutes to really cook down the lentils, which means you'll have to add extra water to prevent the pan from boiling dry.
The resultant soup is a cross between a thin dahl and a thick soup. The tumeric, which I seem to remember is supposed to be good for colds (I just like the taste) gives the whole soup a lovely golden yellow colour.
You could probably do something fancy with browned onions as a garnish, but I had a bit of toast. I can't give up carbs altogether, can I?!

*get one, they are bloody brilliant.