1/4 cup extra virgin olive oil, plus more for garnish
1 medium leek, white and light green parts only, thinly sliced (about 1 cup)
1 large cloves garlic, thinly sliced
2 cups shelled fresh fava beans, skins removed
2 cups cold or room temperature chicken stock (divided)
2 tablespoons minced fresh tarragon or mint
    salt to taste
    freshly ground black pepper, to taste
    Truffle oil, as garnish