Boil up soup, add lentils, cover pot except for a small gap and cook the lentils. At the end of the cooking time remove cover and stir the lentils  often. Peel the onion and chop finely. Mix well creme fraiche with a third of the lentils and puree with a hand blender. Stir in onion, herbs, 1 tsp tomato paste and the remaining lentils.
Season with salt, pepper and crushed garlic.
Slice the baguette, cover with lettuce leaves and then with the lentils spread.