Preheat oven to 140°c. Place a large fry pan on the stove and turn the heat to high. Add the oil and when it's hot, season the venison on all sides and place into the oil. Seal on all sides until golden brown.
Once sealed, place the venison into a roasting tin and add the stock, juniper berries, cinnamon, and bay leaves. Cover tightly with foil and place into the oven for 4-6 hours until the venison is tender and falling apart.
Remove the venison from the stock and leave to cool. Once cool enough to handle, tear into chunky pieces and leave to one side.
Place another large fry pan on the stove and add the diced bacon or pancetta. Cook on a high heat until the bacon fat starts to melt. Add the shallots and cook for 6-8 minutes until the shallots turn translucent. Add the garlic, the chopped and soaked porcini mushrooms, and the picked thyme leaves. Add the duck fat, the tarragon, and the torn venison. Season with salt and pepper, and place into the fridge to cool.
While it's cooling you can make your puree.
Peel the parsnips and cut into ¼ inch cubes. Put the diced parsnip into a saucepan, add the peeled garlic clove, thyme leaves, butter, truffle paste, salt and pepper, and cover with the cream and milk. Allow to cook until the parsnips are extremely tender, about 15 minutes.
Drain off the liquid and keep to one side. Put the cooked parsnips into the blender. Gradually add the cooking liquid until you have a puree the consistency of yoghurt. Check for seasoning, cover the puree with cling film, and leave to one side.
Lay the smaller circles in front of you and brush the edges with the beaten egg. Spoon the venison mixture into a small ramekin or cup (about 100 g worth) and tip into the middle of the pastry disc. Lay the larger disc on top and seal the edges with a fork, trying to make sure you have pushed out all the air.
Brush all over with the beaten egg before placing back into the fridge for 10 minutes. Once cold again, remove from the fridge and score 10-12 crescent shapes from the top of the Pithiviers to the bottom to create a nice swirling pattern before brushing with beaten egg once again. Sprinkle with sea salt before placing in a 190°c oven for 15-20 minutes until golden brown.
Reheat your puree and serve on the bottom of you warm plate. Top with the pithiviers and serve.