Melt the butter in a large nonreactive saucepan. Add the onion and cook over moderately high heat, stirring, until softened and lightly browned, about 6 minutes. Add the honey and cook, stirring for 1 minute. Add the chicken stock, raise the heat to high and boil for 5 minutes. Stir in the spinach and the whole parsley leaves. Bring to a boil and cook until the spinach is tender but still bright green, about 3 minutes. Working in batches, puree the soup in a blender until smooth. Return the soup to the saucepan.