In a bowl, combine all the ingredients with a whisk. Season with salt and pepper. Refrigerate.
In a large pot of salted water, cook the potatoes until tender. Cool the potatoes in ice water. Drain. Cut into quarters or 1-cm (1/2-inch) thick slices. Set aside.
In two pots, bring salted water to a boil. Cook the fiddleheads in one of them for 2 to 3 minutes. Remove and plunge into the second pot for 2 minutes. Cool into ice water. Drain. Set aside.
In a bowl, combine the potatoes and fiddleheads with the oil. Season with salt and pepper. Divide among four plates. Garnish with smoked salmon rosettes. Drizzle with creamy dill dressing and serve with lime wedges.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.