Bring the vegetable stock to the boil, add the lentils and bay leaf, cover and simmer for approx. 10 minutes. Take off the stove, remove the lid, remove the bay leaf, let the lentils evaporate for a few more minutes.
In the meantime, finely chop the onion and garlic. Heat the butter in a small pan, fry the onion, garlic and sesame seeds in it lightly.
Put together with the lentils in a blender jar and puree finely, season with salt and basil.