Slice 6 leeks (white part only) in quarters lengthwise. Clean and pat dry. Heat a large wide frying pan over medium. Add 1 tbsp olive oil, then leeks, 2 tbsp white wine or dry white vermouth, 1 cup vegetable broth and 1/4 cup freshly squeezed lemon juice. Bring to a boil, then reduce heat to medium-low. Simmer, partially covered, until tender, about 15 min. Remove leeks to a plate. Increase heat to high. Boil liquid until slightly reduced, 4 min. Stir in 1 tbsp lemon zest, 1/4 tsp salt and season with pepper. Pour over leeks.