In a saucepan pour 1.5 liters of cold water, add the washed lentils, peeled potatoes and onion coarsely chopped, cloves garlic, salt and spices. Boil until complete softening of the product. Transfer to a suitable container and blend. Wash and dry the pan and heat them in it the oil and the butter, add the flour and fry with constant stirring about 4-5 minutes over medium heat. Pour the flour in about 1 liter of hot water, stir and add the strained nice mixture. We have made a return, stirring constantly. If the soup seem too thick can add more hot water until you get the desired density. If necessary add more salt. Serve with a slice of lemon.