This is a comforting, mellow dish that has just enough zing in it from the capers, anchovies, lemon zest and sour cream to keep everything interesting. I normally use wild pig for these meatballs, but if you are not a hunter, go for ground veal -- if you can find humanely raised veal -- or ground pork.
Heat the 2 tablespoons butter in a small frying pan and cook the cup of onions over medium heat until they are soft. Do not brown them. Sprinkle a little salt over the onions as they cook. When they are translucent and soft, remove from the pan and set aside to cool.
Once the onions are cool, mix all the meatball ingredients together in a bowl. Form into small meatballs with a teaspoon. You can make them bigger, but a heaping teaspoon makes a nice size.
Heat the broth in pot large enough to fit all your meatballs. A wide, deep saute pan with a lid is a good choice. Once the broth is simmering, turn the heat down to as low as it will go and add the meatballs carefully. If they're not all submerged in the broth it will be OK. Cover the pot and let the meatballs cook gently for 25 minutes. Carefully remove them and set them aside.
Pour out the broth and save it. Wipe the pan with a paper towel and set it back on the heat. Add the 3 tablespoons butter and turn the heat to medium-high. Cook the onions until they're translucent. Don't brown them. Add the flour and mix well. Cook this over medium heat, stirring often, until everything is the color or coffee-with-cream. Add the hot broth a little at a time, stirring constantly. Keep adding it until you have a sauce the consistency of thin gravy -- not as thick as Thanksgiving gravy, not thin like soup. You probably will not need the whole quart.
Return the meatballs to the sauce and add the capers. Heat through on low heat, then add the parsley.
Serve with the sour cream at the table. Have people mix it in when they eat. This will prevent the cream from curdling and will let people make the dish as creamy as they want. Grind black pepper over everything and eat!
Notes
Some old recipes for königsberger klopse just say to simmer the meatballs in salted water, but I prefer to use stock or broth. A tip: Do not let the meatballs simmer. Just get the broth to a simmer, carefully drop in the meatballs, cover the pot and turn the heat down to its lowest setting. The meatballs will cook gently, will not fall apart and will remain tender. Serve these with boiled or mashed potatoes or a good German bread.