Soak the bread in the milk in a small bowl to soften.
Put the ground veal in a large bowl and sprinkle with salt, pepper and a few grates of nutmeg. Add the gorgonzola, Parmigiano-Reggiano, sage, garlic and egg. Squeeze the liquid from the bread and crumble it into fine crumbs between your fingertips as you add it to the veal mixture. Drizzle in a little EVOO and gently mix until combined.
Keep a bowl of warm water on hand for rolling the meatballs or use a 2-ounce scoop. Roll or scoop the meat mixture into balls, moistening your hands if not using a scoop, and place on a baking sheet or large plate.
Coarsely chop the escarole into 2-inch pieces.
Bring the stock and 2 to 3 cups water to a low boil in a wide pot. Add the meatballs and simmer until cooked through, 8 to 10 minutes. Add the escarole during the last minute or 2 of cooking and stir until wilted.
Meanwhile, cook the noodles in a pot of boiling salted water until al dente. Drain and add to the soup. Ladle the soup into bowls and top with a few grates of lemon zest.
The soup, without the noodles, can be covered and refrigerated for a make-ahead meal. Add the noodles before serving.