Roast the onion with olive oil in a saucepan.
When onions turn to pink add 1 tablespoon flour and roast little bit more.
Add lentils, carrot and water. Cook until carrot and lentils are soft. Add salt.
In a food processor or blender, whirl the soup until smooth.
It's more delicious if you squeeze some drops of lemon on it or sprinkle some black pepper.