2 leeks (white and light green parts only), thinly sliced |
ADD the mussels to a large saucepan and enough water to cover a quarter of the mussels. Season with salt to taste, then bring to a simmer over medium-high heat. Steam until all the shells have opened, 8 to 10 minutes. Drain and, once cool enough to handle, separate the meat from the shells, discarding the shells. Place the mussels in a bowl.
HEAT the olive oil over medium heat, in a medium saucepan. Add leeks and sweat until translucent, 8 to 10 minutes. Add the onion and carrot, and continue to cook until tender, another 8 to 10 minutes. Season with salt.
CREATE a sachet, while the vegetables are sweating, by combining the coriander seeds, black peppercorns, lemon thyme and jalapeño in cheesecloth secured with butcher's twine.
ADD the sachet, sugar, water and all three vinegars to the vegetables. Bring the mixture to a simmer and cook until slightly reduced, 5 minutes. The vegetables should be tender but not mushy.
REMOVE the sachet from the mixture and discard. Pour the mixture over the mussels and allow to cool at room temperature. Refrigerate overnight, covered, to marinate the meat. The next day, bring to room temperature before serving.
TRANSFER the mussels and vegetables to a serving dish using a slotted spoon. Garnish with olive oil, paprika and dill fronds, then serve with toasted bread and mayonnaise.