Wash the lentils and place them in a pot with 1 ½ liters of water along with the onion, the garlic, the bay leaf and the finely chopped tomato. Let them boil well with the pot half covered until they reduce. Allow them to cool down a bit, remove the bay leaf and add the mixture to the blender. Mix until it is a smooth, velvety pulp. Add half the oil to the pulp, season with salt and pepper, add vinegar and mix for another ½ minute. Serve in plates, with a couple of drops of olive oil in each, and if you wish, accompany with golden croutons as well.