Heat the 2 tablespoons of olive oil in a medium saute pan, add the leek and carrots, and cook over medium heat for 5 minutes. Add the garlic and cook for 1 more minute and set aside.
Meanwhile, place the lentils, 4 cups of water, the onion with the cloves, and the turnip in a large saucepan and bring to a boil. Lower the heat and simmer uncovered for 20 minutes, or until the lentils are almost tender. Remove and discard the onion and turnip and drain the lentils. Place them in a medium bowl with the leek and carrots, and add the butter.
Meanwhile, whisk together the 1/4 cup of olive oil, the mustard, vinegar, salt, and pepper. Add to the lentils, stir well, and allow the lentils to cool until just warm, about 15 minutes. Sprinkle with salt and pepper and serve. The longer the lentils sit, the more salt and pepper you'll want to add.
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