Saute onion in butter until lightly colored about 12 minutes. Soak bread in milk for 10 minutes. Squeeze bread to remove excess milk. Crumble bread and discard milk. Add beef, onions, eggs, ice water, sour cream, salt and pepper. Knead until blended. Set aside. Preheat oven to 375 degrees. In a second bowl, combine eggs, scallions, and melted butter. Season with salt and pepper. Spread meat loaf mixture out on a large piece of waxed paper. Spread stuffing over meatloaf mixture. Leave a 1 inch border on all sides. Roll up like a jelly roll, starting on one long side. Peel back wax paper as you roll. Place seam side down on prepared baking sheet. Spread with mayonnaise using rubber spatula. Sprinkle generously with bread crumbs, sweet and hot paprikas. Bake 1 hour, cut into thick slice and serve at once.