Heat the olive-oil in a large, heavy fry pan with a tight-fitting lid. Sauté the shallots, leeks, and one clove of garlic for a few minutes. Add 3 tablespoons of parsley (reserve remaining tbsp for garnish), vinegar, wine, fennel seeds, and Mezcal/Pernod/Brandy. Heat until almost boiling. Add mussels and steam for 3-5 minutes until the mussels have opened.