Preheat the oven to 180°C.
Remove the mallard legs and breasts and discard the skin.
Clean the duck leg bone and remove the thigh bone while keeping it whole.
Blanch the chopped cabbage in boiling water for 3 minutes then drain.
Fry bacon lardons for 2 minutes and add onion for 1 minute.
Cook the cabbage and garlic with the bacon for 5 minutes.
Layer pancetta over half a crepinette and place duck and cabbage on top.
Roll the crepinette around the duck meat leaving the leg bone exposed.
Encase the parcel in puff pastry with the bone protruding from the side.
Place parcels on a tray and brush with beaten egg yolks.
Bake for 25 minutes and let rest for 10 minutes after removal.
Fry mushrooms in butter for 3 minutes until cooked.
Season the mushroom mixture with salt and pepper.
Spoon mushrooms alongside the sliced mallard en croute to serve.