Preheat the oven to 150°C.
Simmer the duck giblets and stock in a saucepan for 30 minutes.
Fry the lardons in 25g of butter in a large casserole for 2 minutes.
Add button onions and fry for 3 minutes until golden-brown, then set bacon and onions aside.
Prick the ducks with a knife, rub with salt, and fry in the casserole until browned.
Drain the fat, add the strained stock, cover, and braise in the oven for one hour.
Add onions, bacon, carrots, and leeks to the casserole and braise for 15 minutes.
Remove the ducks to rest in a warm place and skim excess fat from the liquid.
Boil the liquid on the hob with herbs, peas, and lettuce until reduced by one-third.
Whisk in the remaining 125g of butter and season with salt and pepper.
Carve the ducks and serve on a plate with the sauce spooned over.