1. Soak the bread crumbs in the milk until the milk is absorbed, about 5 minutes. Melt 1 tablespoon butter in a small skillet over medium heat. Cook the onion in it, stirring, until it is softened, 4 to 5 minutes. Remove from the heat.
2. Mix together the bread crumbs, onion, meat, salt, pepper, parsley, egg, and allspice or cinnamon. Shape into meatballs 1½ inches in diameter. Melt the remaining butter in a large, deep skillet over medium heat. Add the meatballs (you may have to do this in batches; if so, it may be easier to use the oven; see headnote) and cook, shaking gently every couple of minutes. Adjust the heat so that the meatballs brown but the fat does not burn, and cook until they are brown allover. Cook until an instant-read thermometer inserted into the center of a meatball reads 160°F.
3. Remove the meatballs to a platter and keep warm while you prepare the sauce: Pour off all but a tablespoon or two of the fat, then stir in the flour and cook, stirring, for about a minute. Over medium-high heat, add the stock or water and cook, stirring, until the liquid is reduced by about half (If you choose not to use the cream, pour this sauce over the meatballs and serve.)
4. Stir in the cream, reduce the heat to medium-low, and cook, stirring, for about 2 minutes, until the sauce is smooth, golden brown, and slightly thickened. Pour over the meatballs, garnish, and serve.
Leaner Meatballs: Omit bread crumbs, milk, and egg; increase onion and parsley to 1 cup each. Grill, broil, or bake at 400°F until done, 15 minutes or less. Serve without sauce.
Spiced or Herbed Meatballs: To either the master recipe or the lean variation, add 1 tablespoon ground cumin or curry or chili powder; or add 1 tablespoon minced fresh mint leaves, ¼ teaspoon ground cinnamon, and 1/8 teaspoon ground allspice; or substitute fresh dill, chervil, or chives for some or all of the parsley.