Klopsk W Smietanie (meatballs with Sour Cream)

Cut off crusts and in a small bowl saturate the bread in milk. Use a large skillet to saute the onion minced in the butter until soft. Combine well in a large bowl the ground beef, lightly beaten egg yolks, bread mixture, onion, dill, tarragon, salt and pepper. Beat 2 egg whites until they hold soft peaks, fold into beef mixture. Form small balls from beef mixture and sprinkle with flour. Brown meatballs in large skillet using 1/4 cup butter over medium heat. In another skillet saute 1/2 pound sliced mushrooms in 3 tablespoons of butter until browned. Add to meatballs and stir in 1 1/2 cups sour cream, coating the meatballs and coating the meatballs and simmer in the mixture covered partially over low heat for 30 minutes. Stir occasionally. Salt and pepper to taste.