Mix the bread crumbs and milk together in a medium-size bowl. Set aside for 15 minutes to allow the bread crumbs to absorb the liquid. In a separate bowl, combine the ground meats, thyme, garlic, and grated onion. After the meat mixture is combined, form a well in the center of the meat. Pour the beaten egg in the well. Using a fork, mix the bread crumbs into the egg. With your hands, mix all the ingredients together until just combined; don't overwork the meat or the meatballs will be dense. For ease in forming the balls, chill the mixture for 30 minutes.
To form the meat balls, dip your hands into water, then roll the meat into balls about 1 1/2 inch in diameter. This is a soft dough, so don't worry of the meatballs are not perfectly round.
Heat in a large skillet, add the oil, and then add the meatballs to the skillet. Sear the meatballs over medium to high heat for about 3 to 4 minutes. When the meatballs are evenly browned on all sides, add the water to the pan and continue cooking over low heat, shaking the pan occasionally, for 10 minutes, or until the meat is cooked through. Serve warm or at room temperature, with a lingonberry or cranberry relish.