Serve this vegetarian appetizer as you would caviar; place a spoonful of glistening Beluga lentils atop a cracker, then add a tangle of caramelized onions and a bit of crème fraîche. Beluga lentils are similar to common varieties in taste and cooking technique but turn glossy once properly cooked. You can substitute French green lentils for Belugas. The lentils and onions can be prepared up to one day in advance, but be sure to bring to room temperature for serving. Prep: 20 minutes; Cook: 1 hour 5 minutes; Stand: 1 hour 20 minutes.