Smoked Trout with Root Vegetable Rémoulade

Name: Smoked Trout with Root Vegetable Rémoulade
Ingredients: 1 1/4 cups crème fraîche; 3 tablespoons French whole-grain mustard (such as Maille); 3 tablespoons fresh lemon juice; 3/4 teaspoon fine sea salt, plus more to taste; 1 1/2 pounds mixed root vegetables (such as celery root, parsnips, orange and yellow carrots, kohlrabi, golden beets, watermelon radishes, and black radishes); 4 ounces smoked trout; 1/4 cup chopped fresh flat-leaf parsley or 1/2 cup fresh chervil leaves; 1 cup nasturtium leaves or watercress leaves