Seared Hake with Baby Potatoes and Green Sauce

Name: Seared Hake with Baby Potatoes and Green Sauce
Ingredients: 1/3 cup fresh celery juice (from about 2 stalks); 1/3 cup fresh sorrel or cilantro juice (from about 2 cups, lightly packed); 2 teaspoons fresh leek juice (from about 1 dark-green leek top); 1 tablespoon white wine vinegar or lemon juice; Kosher salt; 1 pound peanut potatoes or baby potatoes (as small as possible); 3 tablespoons olive oil, divided, plus more for drizzling; 4 4-ounce pieces skin-on hake or cod fillet; 4 scallions, trimmed; 1/2 cup plain Greek yogurt; Chervil or other tender herb sprigs (for serving)