How to Make It
In a medium saucepan, combine the wine, water, smashed garlic, celery, red bell pepper, onion and bay leaf and bring to a boil. Cover and simmer for 3 minutes. Add the mussels, cover and cook over high heat for 3 to 5 minutes; remove the mussels to a bowl as they open. Strain the cooking liquid and return it to the pan. Remove the mussels from their shells and transfer to a bowl.
If using green beans, blanch them in the reserved mussel cooking liquid until bright green and tender, about 2 minutes. Remove the beans with a slotted spoon, pat dry and let cool completely. Cut the beans into 1 1/2-inch lengths.
In a bowl, whisk the oil with the vinegar, tarragon, mustard and minced garlic. Season with salt and pepper.
Add the sea beans or green beans to the mussels and toss with 3 tablespoons of the vinaigrette. Season with salt and pepper. Toss the romaine with the remaining vinaigrette; mound on plates, top with the mussel salad and serve.
Sea beans are available at Melissa's Specialty Produce, melissas.com