Coat the venison chunks with the flour and salt and pepper.
Heat 2 tbsp oil in ovenproof casserole and brown the meat in batches until evenly browned, about 2 minutes each side.
Transfer to a bowl.
Add the leeks, onions and carrots to the casserole with a little more oil and stir over medium heat for 4 to 5 minutes, until colored.
Add the mushrooms and rosemary and cook for about a minute. Pour in the wine, scraping the bottom of the pan with a wooden spoon to deglaze. Bubble until reduced right down.
Pour in the stock and bring to a simmer.
Return the venison, with any juices released, to the pan. Partially cover with a lid and gently braise for 40 to 50 minutes, until venison is tender., giving the mixture a stie every once in a while.
About 15 minutes before venison will be ready, slice the new potatoes into 1/2 inch thick circles. Season and cook in a little olive oil in a wide non-stick skillet until golden brown on both sides. Add to the casserole to finish cooking.
Once the potatoes and venison are tender, remove the pan from heat and let cool slightly.
For the topping, peel the potatoes and cut into 2 inch chunks.
Cook in a pan of salted water for 15 minutes or until tender.Drain and mash with potato ricer back into the pan.
While still hot, add the butter, cheese and seasonings. Mix well to combine. Cool slightly, then mix in the egg yolks.
Heat the oven to 425 degrees F.
Tip the venison mixture into large pie dish or shallow cast iron pan and top with the mash. Rough up the surface with a fork.
Bake for 20 minutes, until top is golden and the filling is bubbling around the sides.