Soak roll in cold water for 10 minutes. Squeeze, pick to pieces, and mix with ground meat in a bowl. Chop speck, anchovies, and peeled onion. Add to ground meat. Add egg. Mix thoroughly; season with salt and pepper. Bring water, stock and wine with salt, bay leaf, and the halved peeled onion to a boil. From the meat mixture, form small balls about 4 cm in diameter and add to the liquid. Let simmer covered for 20 minutes on low heat. Remove with a skimmer, and keep warm in a preheated bowl. Strain broth and also keep warm. For the sauce, melt butter in a pot. Add flour, and lightly sauté for 3 minutes while constantly stirring. Deglaze with about 1/2 l broth as needed while still stirring.
Add lemon juice, capers as needed, and mustard. Mix egg yolk with a little bit of sauce, and add to the remaining sauce. Season with sugar, salt, and pepper. Add meatballs and lightly heat up.