Trim as much membrane and any tough parts from the venison leg as possible. Cut it into 3 large pieces, sawing through the bone if needed.

Brown the meat on all sides in hot oil and butter. Season with salt and pepper, add the broth, and bring to a simmer.

If you have the right equipment, use a cast iron Dutch oven to brown the meat, then place it directly in the oven at 195°F (90°C) with the broth. If not, use an oven-safe dish and wrap the meat and broth in parchment paper. Either way, cook for at least 4 hours at 195°F (90°C).

For the mashed potatoes, cook the potatoes in salted water, then mash them. Add a generous amount of butter, the cream, salt, pepper, and grated nutmeg.

Wash and dice the carrots, then cook them in the potato water.

Wash the mushrooms and chop them by hand or with a food processor.

Finely chop the onions and shallots.

Sauté the onions and shallots in oil. Once translucent, add the mushrooms. Cook for a few minutes, then add the cooked carrots. Season with salt and pepper, then set aside.

Once the meat is cooked and cooled, shred it with a fork or by hand. Discard the remaining bones and membranes.

Add the meat to the vegetables, mix well, and spread the mixture in the bottom of a baking dish, pressing it down firmly. (You may only need half the meat; save the rest for another pie if you have too much.)

Spread the mashed potatoes on top and smooth with a spatula.