Wash the lemons. Squeeze 2 of the lemons and cut the other 2 into small wedges, removing the pips.
Soak the bread roll in water. Peel and dice the onion. Heat the butter and sweat the onion until translucent. Add the thyme. Combine the mince with the onion, egg, mustard, salt, pepper, sausagemeat and the squeezed-out bread roll and mix well. If the mixture is too soft knead in a few breadcrumbs.
Using moistened hands form the mixture into small balls (approximately 16). Heat the oil in a frying pan and quickly brown the meatballs on all sides.
Add the lemon pieces, fry briefly, then add the lemon juice, white wine and bay leaves and simmer over a low heat for about 10 minutes.
Season to taste with salt and pepper and serve with potatoes.