Bring a 4-qt. saucepan of salted water to a boil. Cook carrot and leek until soft, 3–5 minutes; transfer to an ice bath until cold, then drain and set aside. Whisk cream, flour, chives, dill, parsley, piment d'Espelette, curry powder, eggs, lemon zest and juice, and salt in a bowl until smooth. Fold in reserved carrot and leek, and the scallops; set aside.