Bring a medium pot of salted water to a boil over high heat, add the pearl onions and cook 3 minutes. Remove with a slotted spoon, pat dry and set aside.
Melt the butter in a large Dutch oven over medium heat, stir in the flour, nutmeg and some salt and pepper and cook until the flour is well incorporated and the raw flavor cooks out, 3 to 4 minutes.
Add the cream and chicken stock, bring to a boil, then lower the heat and simmer until thickened, 6 to 8 minutes. Add the pearl onions, then the kale, little by little, and cook until it wilts, about 5 minutes. Remove the pot from the heat, stir in the Parmesan, taste, and adjust seasonings. Serve hot.