In a large pot, heat a tablespoon of olive oil over medium heat. Chop onion and garlic and add to the pot. Sauteé until translucent, about 2 minutes. Add white wine or vegetable broth, a pinch of cayenne, salt and black pepper. Add mussels to the pot and cover with a lid. Cook for 5-6 minutes, shaking the covered pot occasionally. They are ready once they all open. Discard any closed mussels. Transfer mussels to a serving bowl and garnish with minced parsley. Serve at once with lemon wedges, fresh ciabatta and white wine if desired.