In a 3-quart saucepan over high heat, combine the lentils with 4 cups water and bring it to a boil. Skim and discard any foam and add the bay leaf. Reduce the heat to low, cover the pan, and simmer until the lentils are tender, about 30 minutes; drain.
While the lentils simmer, in a small saute pan over medium heat, warm the oil. Add the onion and pine nuts and cook until the onion softens and the pine nuts begin to color, about 5 to 7 minutes. Stir in the garlic, tomato paste, coriander, caraway, cumin, cayenne, and salt. Continue to cook for 5 minutes. Stir in the lemon juice, scraping up any browned bits on the bottom of the pan. Remove from the heat.
In a food processor, add the lentils and onion mixture and puree until smooth.
Transfer to a serving bowl and serve at once. May be covered and chilled and served cold. Serve with pita toasts or crudite.